Improvements in or relating to closures

Abstract

 A cap 1 for closing an aperture in a reservoir for fluid in an automobile brake, coolant or power steering system comprises an inner cap member 2 for securing over the aperture and an outer cap member 3. The inner and outer cap members 2,3 have co-operating formations 10,16 which interlock when the outer cap member 3 is rotated in a direction to release the cap 1. The formations 10,16 provide frictional engagement when the outer cap member 3 is rotated in the opposite direction up to a threshold torque to secure the cap 1. The outer cap member 3 is rotatable relative to the inner cap member 2 when the threshold torque is exceeded to prevent over-tightening of the cap 1 and to enable the circumferential orientation of the outer cap member 3 relative to the inner cap member 2 to be adjusted when the cap is secured 1.

Description

[0001] This invention concerns improvements in or relating to closures. In particular it relates to caps designed to close off an aperture of a container. It has particular, but not exclusive, application to caps for use in the automobile field to cover and secure apertures of fluid reservoir containers, for example for brake, coolant and power steering systems.

[0002] Caps, lids, and other closure devices are used on a massive scale and on a daily basis world-wide. If well designed they allow easy user access into a container while preventing spillage of the contents from the container during transport or storage of the container.

[0003] There are a variety of ways in which the cap may be joined to the container but it is usually rotatably driven onto the container via a screw thread. The tightness or security of the attachment between the cap and the container then depends on the torque applied to the cap when securing it on the container. If excessive torque is applied, the cap may be done up very tightly and thus be difficult to undo.

[0004] A particular application where this may be a problem is in relation to caps used to cover apertures of fluid reservoirs in automobiles. In these applications the aperture is situated amongst parts of the engine and may be difficult to reach. It may therefore be difficult or impossible for an elderly or disabled person to undo a cap that has been overtightened. Furthermore, as the container is surrounded by other structures, it may not be possible to use torque-assist devices on the cap to make it easier to loosen.

[0005] A further problem arises where the cap bears a logo or symbol presenting information to the user which may be advantageously presented in an upright position so as to be readily seen and understood by the user. With caps having a screw thread, however, the circumferential orientation of the cap depends on the degree to which the cap has been tightened on the container. Over a period of time, repeated overtightening may cause wear of the screw thread on the cap and/or the container affecting the circumferential orientation of the cap. As a result, the initial pre-set position of the cap in relation to the container may change, leading to information on the cap being in an uncertain or indefinite orientation.

[0006] The present invention addresses the problems with these previous cap designs. It aims to do so whilst still providing a cap which is highly functional, economical to manufacture and appealing to use.

[0007] According to a first aspect, this invention provides a cap for closing an aperture comprising an inner cap member which is rotatably securable around the aperture and an outer cap member co-operable with the inner cap member to secure the cap over the aperture wherein the inner cap member is rotatable with the outer cap member to secure the cap until a torque applied to the outer cap member exceeds a threshold value above which the outer cap member is rotatable relative to the inner cap member.

[0008] The outer cap member may therefore be used to tighten the inner cap member on the aperture up to the threshold torque. In other words, the user drives the outer cap member which in turn drives the inner cap member onto the aperture.

[0009] Once the threshold torque is exceeded the co-operation between the outer cap member and the inner cap member is overcome and the outer cap member rotates around the inner cap member. A cap in accordance with this invention cannot therefore be overtightened by an excessive torque applied to the outer cap member by the user.

[0010] Such rotation of the outer cap member without further tightening of the inner cap member enables the circumferential orientation of the outer cap member relative to the inner cap member to be adjusted when the cap is secured. In this way, the outer cap member can be re-positioned in the same position each time the cap is secured so that any information on the outer cap member is presented so as to be readily seen and understood by the user.

[0011] Preferably, the inner cap member and outer cap member have respective surface formations which provide frictional co-operation when the outer cap member is rotated in a direction to secure the cap until the threshold torque is exceeded, thereby overcoming the frictional engagement between the cap members and allowing the outer cap member to rotate relative to the inner cap member. In this way, overtightening of the inner cap member is prevented and the outer cap member can be adjusted to any desired angular orientation.

[0012] In a preferred embodiment the surface formations comprise saw tooth formations on one cap member and flexible finger formations on the other cap member. These provide a convenient and easy to manufacture means of co-operation between the cap members.

[0013] Advantageously, the flexible finger formations and the saw tooth formations project in opposite senses. In this way, when the inner cap member and the outer cap member are assembled, a ramp face of the saw tooth formations compresses the flexible finger formations to provide the frictional co-operation between the cap members. The frictional co-operation enables the user to drive the inner cap member on to the aperture via the outer cap member until the rotational torque applied to the outer cap member exceeds the slip torque of the frictional co-operation between the cap members.

[0014] If further torque is applied in the direction to secure the cap, the outer cap member will then slip around the inner cap member. This produces an audible noise in the form of a series of clicks as the flexible finger formations ride over the saw tooth formations thereby indicating to the user that the threshold torque has been exceeded and the cap is secured.

[0015] The outer cap member may thus be positioned to maintain its original or pre-set orientation with respect to the user when the cap is secured whatever the orientation of the inner cap member.

[0016] The outer cap member may carry information, either in the form of a label stuck to the cap member or, in a preferred embodiment, printed, moulded or otherwise formed directly on to the cap member. This information may be an aesthetic design and/or may relate to the contents of the container, the mechanism for removing the cap or the method of filling the container. A particular design could, for example, comprise a hazard warning symbol.

[0017] The designs are advantageously presented to the user in a correct orientation so that they may easily be read and their importance is immediately apparent. This is especially beneficial where international symbols are used with no textual content such that the symbols may not be meaningful if presented in the wrong orientation. Additionally, some symbols or other designs have no obvious correct orientation and may confuse the user or be misrepresented if presented in an incorrect orientation. This is particularly so if the design of the symbol relates to the functional aspects of the design of the cap. The resulting confusion may lead, for example, to the user attempting to remove the cap in an incorrect manner.

[0018] It may also be necessary to align a point on the cap with a particular point on the container, in order, for example, to operate the opening or closing mechanism of the cap. In this situation it is also highly advantageous to be able to rotate the cap to a particular alignment.

[0019] Preferably, to remove the cap from the container, the outer cap member is turned in the opposite direction so that a projecting end of each flexible finger formation may then interengage with an abutment face of the saw tooth formations to lock the cap members for rotation of the outer cap member in a direction to remove the cap. This provides a secure connection between the inner and outer cap members so that as much torque as necessary may be applied to the outer cap member to remove the cap from the aperture.

[0020] Preferably, the saw tooth formations are circumferentially spaced around an outer surface of the inner cap member and the finger formations are circumferentially spaced around an opposed inner surface of the outer cap member. In a preferred embodiment, there are half as many finger formations on the outer cap member as there are saw tooth formations on the inner cap member. In this way, the finger formations engage with every other saw tooth formation.

[0021] Advantageously, the number and spacing of the co-operating formations is chosen so that the outer cap member can be indexed on the inner cap member. In a preferred embodiment, there are twenty four saw tooth formations uniformly spaced apart in a circumferential direction providing an indexing movement in the region of 15° between successive saw tooth formations. Alternatively, the spacing of the saw tooth formations may be altered to vary the indexing movement and provide a much finer or much coarser indexing angle according to the nature of the information on the cap and the angular adjustment required.

[0022] Preferably, the inner cap member is securable over the aperture and the outer cap member is securable over the inner cap member. The outer cap member may substantially cover the inner cap member in use. In this way, the outer cap member provides the physical cover for the aperture and conceals and protects the inner cap member.

[0023] In a preferred embodiment, the outer cap member comprises a generally cylindrical side wall closed at one end by an end wall provided with a projection on the underside in the form of an annular wall concentric with the side wall, and the inner cap member comprises a substantially cylindrical side wall concentric with and spaced from the side wall of the outer cap member and having an end wall at one end and an external annular flange at the other end.

[0024] Preferably, the projection on the underside of the end wall of the outer cap member is a snap fit in an aperture in the end wall of the inner cap member, and the flange of the inner cap member is a snap fit in a circumferential groove extending around the side wall of the outer cap member remote from the end wall.

[0025] In this way, the cap members are axially secured relative to each other while allowing rotation of the outer cap member relative to the inner cap member. Furthermore, the co-operating formations on the opposed surfaces of the side walls of the cap members are concealed and protected by the engagement of the external flange of the inner cap member in the circumferential groove of the outer cap member.

[0026] The outer cap member advantageously further comprises grip formations on the outer surface of the side wall. The grip formations may comprise longitudinal ribs circumferentially spaced around the side wall. In a preferred embodiment, there are equal numbers of ribs and finger formations, and each rib corresponds to a respective position of each finger formation. This provides the user with an indication of the indexing movement of the cap.

[0027] The inner surface of the side wall of the inner cap member is preferably screw threaded for engagement with a complementary screw thread on the container for securing the cap over the aperture to be closed by the cap.

[0028] The end wall of the inner cap member may provide a seating for a separate seal, for example a washer, of elastomeric or other suitable resilient material located over the projection on the underside of the end wall of the outer cap member and arranged for sealing engagement with the container when the cap is secured over the aperture.

[0029] Alternatively, the end wall of the inner cap member may be provided with an integral seal, for example a raised annular rib, concentric with the projection on the underside of the end wall of the outer cap member and sized and shaped for sealing engagement with the container when the cap is secured over the aperture. The rib may be V-shaped in cross-section.

[0030] The cap members may be constructed and arranged to provide a fluid tight seal with the container when the cap is secured over the aperture. For certain applications, however, it may be desirable to provide a leak path for a gas, usually air, to pass into and out of the container when the cap is secured over the aperture while preventing ingress of liquid, usually water or egress of liquid from the container.

[0031] Thus, the cap may maintain a substantially liquid tight seal while providing controlled gas flow into and out of the container. This is particularly important when the cap is used to close an aperture in a reservoir of a vehicle braking system. Allowing the ingress and egress of gas prevents a vacuum developing in the brake fluid reservoir. This highly undesirable event would prevent safe operation of the braking system. At the same time, the entrance of water into the brake fluid reservoir, for example from rain or when washing the vehicle, and/or the escape of brake fluid which would have an adverse affect on the performance of the braking system is also prevented.

[0032] The leak path is preferably arranged so that gas can pass between the cap members. For example, one or both of the cap members may be provided with formations providing a tortuous passageway through which gases such as air can flow but which prevents or substantially restricts flow of liquids. In a preferred embodiment, the end wall of the inner cap member may be provided with a series of raised annular ribs on the outer surface concentric with the projection on the underside of the end wall of the outer cap member and provided with discrete notches to define a labyrinth like tortuous passageway.

[0033] The inner and outer cap members may be made of a plastics material, preferably a thermoplastics material. This enables an attractive, practical and inexpensive cap to be produced. The cap components may be manufactured by a moulding process, preferably injection moulding. Appropriate design of the mould then enables the surface formations to be integral to the main structure of the associated cap member. In this way, the cap may be formed from two parts only which are readily assembled.

[0034] According to a second aspect, this invention provides a reservoir container in combination with a cap according to the first aspect.

[0035] In a preferred embodiment the reservoir container houses fluid. This fluid may be suitable for a particular application for example in an automobile brake, coolant or power steering system.

[0036] Embodiments of the present invention will now be described by way of example only, with reference to the following drawings in which:-

FIGURE 1 shows schematically an exploded side perspective view of an embodiment of the inner cap member and outer cap member;

FIGURE 2 shows schematically an alternative embodiment where the outer cap member is secured in the inner cap member, the assembly incorporating a separate sealing means;

FIGURE 3 shows schematically a side perspective view of the outer cap member secured on the inner cap member and providing an integral seal;

FIGURE 4 shows schematically a variety of detailed views of the inner cap member of the embodiment of Figure 1, of which:

Figure 4a shows schematically a plan view from the bottom;

Figure 4b shows schematically a top plan view;

Figure 4c shows schematically a plan view from the side;

Figure 4d shows schematically a section view through the line A-A in Figure 4b;

Figure 4e shows a detail, to an enlarged scale, of the integral seal;

Figure 4f shows a detail, to an enlarged scale, of one of the saw tooth formations; and

FIGURE 5 shows schematically a variety of detailed views of the outer cap member of the embodiment of Figure 1 of which:

Figure 5a shows schematically a top plan view;

Figure 5b shows schematically a bottom plan view;

Figure 5c shows schematically a plan view from the side;

Figure 5d shows schematically a section view through the line A-A in Figure 5b;

Figure 5e shows a detail, to an enlarged scale, of one of the flexible finger formations;

Figure 5f shows a detail, to an enlarged scale, of the end wall projection;

Figure 5g shows a detail, to an enlarged scale, of the side wall groove.

[0037] Referring to the drawings, Figure 1 shows a cap 1 for closing an aperture of a container (not shown) such as a fluid reservoir for a brake, coolant or power steering system of an automobile (not shown). The cap 1 comprises an inner cap member 2 which is rotatably received within an outer cap member 3. In this embodiment, the cap members 2,3 are mouldings of plastics material.

[0038] Figures 1 and 4a to 4f in which like numbers indicate like parts show that the inner cap member 2 has a continuous side wall 4 which forms a cylinder. An annular flange 5 extends outwardly from end 4a of side wall 4 and an end wall 6 is provided at end 4b of side wall 4. The end wall 6 has an aperture 7 in its centre with the edge of the aperture 7 being concentric with the side wall 4.

[0039] The inner cap member 2 is provided with an internal screw thread 8 on the side wall 4 for co-operation with an external screw thread on a wall (not shown) surrounding the aperture in the container to be closed.

[0040] The flange 5 is provided with cut outs 5a in the free edge and the end wall 6 is provided with cut outs 6a in the marginal edge of the aperture 7. The outer surface of end wall 6 is provided with concentric ribs 9 defining annular channels connected by discrete notches 9a.

[0041] The ribs 9 space end wall 6 of the inner cap member 2 from the outer cap member 3 and together with the cut outs 5a,6a provide a tortuous route by which gases can pass into and/or out of the container when the aperture is closed by cap 1 while substantially preventing passage of liquids into or out of the container.

[0042] For example, in the application of the cap 1 to a brake fluid reservoir for vehicle braking system, it is important that air can pass into and out of the reservoir to prevent a vacuum being created in the reservoir while precluding entry of water or escape of brake fluid which would reduce the efficiency of the brake system.

[0043] The outer surface of the side wall 4 of the inner cap member 2 is provided with a number of saw tooth projections 10 which all extend in the same sense around the circumference of the inner cap member 2. Each projection 10 has a ramp face 10a extending generally tangentially and an abutment face 10b extending generally radially for a purpose to be described later. As shown in Figure 4f, the ramp face 10a is inclined at an acute angle of approximately 19/20° with respect to a line normal to the abutment face 10b.

[0044] Figures 1 and 5a to 5d in which like numbers indicate like parts show that the outer cap member 3 has a continuous side wall 11 which forms a cylinder and an end wall 12. The side wall 11 is provided with an annular rim 13 extending outwardly therefrom at the end remote from the end wall 12. The outer surface of the side wall 11 is provided with a number of projections 14 which assist the user in the gripping of the outer cap member 3.

[0045] The inner surface of the end wall 12 is provided with a projection 15 in the form of an annular wall concentric with side wall 11. The annular wall projection 15 is provided with cut outs 15a in the outer surface thereof which, like the cut outs 5a,6a, aid the flow of gases into and/or out of the container when the cap 1 is in position while restricting or preventing flow of liquids into or out of the container. As shown in Figure 5f, the wall projection 15 has an external lip 15b around the free edge and an external recess 15c around the base.

[0046] The inner surface of the side wall 11 is provided with finger projections 16 which extend in the same sense around the inner circumference of the side wall 11 and are also joined to the end wall 12. The finger projections 16 extend in the opposite sense to the saw tooth projections 10 on the inner cap member 2 and are half as many in number. As best shown in Figure 5e, each finger projection 16 is inclined at an acute angle of approximately 15° with respect to a line parallel to a tangent at the base of the finger projection 16.

[0047] Figures 2 and 3 show the inner cap member 2 received within the outer cap member 3. The marginal edge of the aperture 7 in the end wall 6 of the inner cap member 2 is a snap fit in the external recess 15c at the base of the annular wall projection 15 of the outer cap member 3, and the outwardly extending flange 5 of the inner cap member 2 is a snap fit in an annular groove 11a (Figure 5g) provided in the inner surface of the side wall 11 of the outer cap member 3. In this way, the cap members 2,3 are positively secured together so as to prevent axial separation while allowing relative rotation as described later.

[0048] In the embodiment shown in Figure 2, the inner surface of the end wall 6 of the inner cap member 2 is provided with a separate seal in the form of a flat disc-shaped washer 17 which fits over the projection 15 and is retained by the annular lip 15b. The washer 17 is made of resilient material such as natural or synthetic rubber and forms a seal with the container around the aperture to be closed when the cap 1 is secured.

[0049] Alternatively, as shown in the embodiment of Figure 3 and Figure 4, the inner surface of the end wall 6 of the inner cap member 2 is provided with an integral seal in the form of a annular projection 18 concentric with the aperture 7. As shown in Figure 4e, the projection 18 is V-shaped. The projection 18 is arranged to form a seal with the container around the aperture to be closed when the cap 1 is secured.

[0050] In use, the inner cap member 2 is rotatably received within the outer cap member 3 by means of the snap-fit engagement described above. The cap 1 is then used to close the aperture of a container by screwing the cap 1 onto the wall surrounding the aperture of the container which includes an external screw thread corresponding to the internal screw thread 7 of the inner cap member 2.

[0051] The cap 1 is screwed onto the wall surrounding the aperture of the container by the application of torque to the outer cap member 3. The finger projections 16 of the outer cap member 3 co-operate with the saw tooth projections 10 of the inner cap member 2 causing the inner cap member 2 to rotate with the outer cap member 3 enabling the screw thread 7 to engage the corresponding screw thread on the wall surrounding the aperture to secure the cap 1 to the container and close the aperture.

[0052] More particularly, the finger projections 16 are flexible and are arranged to ride up the ramp faces 10a of the saw tooth projections 10 when the outer cap member 3 is rotated in a direction to secure the cap 1. This causes the finger projections 16 to be compressed radially to provide frictional engagement coupling the cap members 2,3 together for rotation of the inner cap member 2 with the outer cap member 3 to secure the cap 1 over the aperture.

[0053] As the cap is tightened, the torque which must be applied to the outer cap member 3 increases. The inner cap member 2 rotates with the outer cap member 3 to tighten the cap 1 until a threshold value is reached corresponding to the slip torque between the cap members 2,3. When the torque applied to the outer cap member 3 exceeds the threshold value, the frictional engagement between the cap members 2,3 is overcome and the outer cap member 3 rotates relative to the inner cap member 2 preventing further tightening of the cap 1 over the aperture.

[0054] As the outer cap member 3 rotates relative to the inner cap member 2, the finger projections 16 of the outer cap member 3 slip over the saw tooth projections 10 of the inner cap member 2 producing a noise or sound in the form of a series of audible clicks as the finger projections 16 clear the ramp faces 10a of the saw tooth projections 10 releasing the radial compression. This warns the user that the desired tightness has been achieved.

[0055] The application of further torque to the outer cap member 3 simply results in the rotation of the outer cap member 3 around the inner cap member 2 which allows the outer cap member 3 to be aligned to a desired orientation, for example if the outer cap member 3 contains information, instructions or warnings. For example, the outer surface of the end wall 12 of the outer cap member 3 may be provided with information on the contents of the container and/or symbols providing instructions or warnings to the user. Such information, instructions or warnings may be provided by attaching a label to the outer cap member or by printing directly on the outer cap member 3.

[0056] In this embodiment, the inner cap member 2 has twenty four saw tooth formations 10 uniformly spaced apart around the side wall 6 providing an indexing movement of the outer cap member 3 of approximately 15° between audible clicks. It will be understood that this indexing movement may be altered by changing the number of saw tooth formations 10 to increase or reduce the indexing angle for finer or coarser adjustment of the outer cap member 3 as desired.

[0057] Similarly, in this embodiment there are twelve finger formations 16 uniformly spaced apart around the side wall of the outer cap member 3 and it will be understood this number may also be increased or decreased as desired.

[0058] The cap 1 is unscrewed from the wall surrounding the aperture when it is desired to open the container by the application of reverse torque to the outer cap member 3. Again, the finger projections 16 co-operate with the saw tooth projections 10 causing the inner cap member 2 to rotate with the outer cap member 3 to release the threaded connection between the inner cap member 2 and the container.

[0059] More particularly, the flexible finger formations 16 ride down the ramp faces 10a when the outer cap member 3 is rotated in a direction to unscrew the cap 1. This releases the radial compression of the finger formations 16 until the finger formations 16 engage the abutment faces 10b of the saw tooth projections 10 causing the cap members 2,3 to be locked together such that rotation of the outer cap member 3 is transmitted to the inner cap member 2 enabling the cap 1 to be unscrewed and removed.

[0060] As will now be appreciated, the present invention provides a cap for closing an aperture in a container that allows the cap to be adjusted to any desired orientation without overtightening the cap. In this way, the cap can be secured so that any markings, data or other information provided on the cap is always presented to the user in the desired orientation while allowing the cap to be removed when required. As a result, the risk of damage to the cap and/or container from excessive torque applied to the cap is avoided.

[0061] It will be understood that the invention is not limited to the embodiment above-described and that various modifications can be made without departing from the concept of the invention. For example, the finger formations 16 may be provided on the outer surface of the side wall 4 of the inner cap member 2 and the saw tooth formations 10 provided on the inner surface of the side wall 12 of the outer cap member 3.

[0062] Alternatively, other types of co-operating surface formations may be employed that interengage only up to a certain torque for rotation of the outer cap member 3 in a direction to secure the cap 1 and are then released for rotation of the outer cap member 3 relative to the inner cap member 2 while locking the cap members 2,3 together for rotation of the outer cap member 3 in the opposite (reverse) direction to release the cap 1.

[0063] The cap 1 may be constructed to provide a leak path for flow of gases into or out of the container as described or to provide a completely fluid tight seal where such ingress or egress of gases is not required. For example, the end wall 6 of the inner cap member 2 may be continuous so as to close the inner end of the inner cap member 2. In this arrangement, the projection 15 on the underside of the end wall 12 of the outer cap member 3 may be received in a blind recess in the upper surface of the end wall.

[0064] Other modifications will be apparent to those skilled in the art and are deemed within the scope of the invention. Furthermore, while the invention has been particularly described for application of the cap to reservoir containers used in automobiles, it will be appreciated that the invention is not limited to such application and that the invented cap may be used with any type of container where it is desired to prevent the cap being overtightened and/or to allow the cap to be located in a particular orientation when secured.

Claims

1. A cap (1) for closing an aperture comprising an inner cap member (2) which is rotatably securable around the aperture and an outer cap member (3) co-operable with the inner cap member (2) to secure the cap (1) over the aperture wherein the inner cap member (2) is rotatable with the outer cap member (3) to secure the cap (1) until a torque applied to the outer cap member (3) exceeds a threshold value above which the outer cap member (3) is rotatable relative to the inner cap member (2).

2. A cap according to claim 1 characterised in that the inner cap member (2) and outer cap member (3) have respective formations (10,16) which provide frictional co-operation when the outer cap member (3) is rotated in a direction to secure the cap (1) until the threshold torque is exceeded, thereby overcoming the frictional engagement between the cap members (2,3) and allowing the outer cap member (3) to rotate relative to the inner cap member (2), for example the formations may comprise saw tooth formations (10) on one cap member and flexible finger formations (16) on the other cap member.

3. A cap according to claim 2 characterised in that the flexible finger formations (16) and the saw tooth formations (10) project in opposite senses whereby a ramp face (10a) of the saw tooth formations (10) compresses the flexible finger formations (16) to provide the frictional co-operation between the cap members (2,3).

4. A cap according to claim 2 or claim 3 characterised in that the formations (10,16) are arranged to produce an audible noise when the threshold torque is exceeded for example by the flexible finger formations (16) riding over the saw tooth formations (10).

5. A cap according to any one of claims 2 to 4 characterised in that the formations (10,16) are arranged to interlock the cap members (2,3) when the outer cap member (3) is rotated in the opposite direction to remove the cap (1) from the container, for example each flexible finger formation (16) may engage an abutment face (10b) of the saw tooth formations (10) to lock the cap members (2,3) for rotation in a direction to remove the cap (1).

6. A cap according to any one of claims 2 to 5 characterised in that the saw tooth formations (10) are circumferentially spaced around an outer surface of the inner cap member (2) and the finger formations (16) are circumferentially spaced around an opposed inner surface of the outer cap member (3), and preferably there are half as many finger formations (16) on the outer cap member (3) as there are saw tooth formations (10) on the inner cap member (2).

7. A cap according to any one of claims 2 to 6 characterised in that the number and spacing of the formations (10,16) is chosen so that the outer cap member (3) can be indexed on the inner cap member (2), for example twenty four saw tooth formations (10) uniformly spaced apart in a circumferential direction providing an indexing movement in the region of 15° between successive saw tooth formations (10).

8. A cap according to any one of the preceding claims characterised in that the inner cap member (2) is securable over the aperture, for example by engagement of co-operating screw threads, and the outer cap member (3) is securable over the inner cap member (2), for example by snap engagement of co-operating locating formations, and preferably substantially covers the inner cap member (2).

9. A cap according to claim 8 characterised in that the outer cap member (3) comprises a generally cylindrical side wall (11) closed at one end by an end wall (12) provided with a projection (15) on the underside in the form of an annular wall concentric with the side wall (11), the inner cap member (2) comprises a substantially cylindrical side wall (4) concentric with and spaced from the side wall (11) of the outer cap member (3) and having an end wall (6) at one end and an external annular flange (5) at the other end, further characterised in that the projection (15) on the underside of the end wall (12) of the outer cap member (3) is a snap fit in an aperture (7) in the end wall (6) of the inner cap member (2), and the flange(5) of the inner cap member (2) is a snap fit in a circumferential groove (11a) extending around the side wall (11) of the outer cap member (3) remote from the end wall (12).

10. A cap according to any one of the preceding claims characterised in that the outer cap member (3) is provided with external grip formations (14), for example longitudinal ribs (14) circumferentially spaced around an outer surface of the outer cap member (3), and preferably the spacing of the ribs (14) corresponds to indexing movement of the outer cap member (3) relative to the inner cap member (2).

11. A cap according to any one of the preceding claims characterised in that the inner cap member (2) is provided with a seal, for example a separate washer (17) or an integral annular rib (18), arranged for sealing engagement with the container when the cap (1) is secured over the aperture.

12. A cap according to any one of the preceding claims characterised in that a substantially liquid tight seal is provided when the cap (1) is secured over the aperture, and the cap members (2,3) preferably provide a leak path for gas, for example air, to pass into and out of the container when the cap (1) is secured over the aperture, for example one or both of the cap members (2,3) may be provided with formations (9;5a,6a) providing a tortuous passageway through which gases such as air can flow but which prevents or substantially restricts flow of liquids.

13. A reservoir container for fluid in an automobile brake, coolant or power steering system, the reservoir having an aperture and a cap (1) according to any one of the preceding claims for closing the aperture.

Drawing