This invention relates to a circular crystal for a watch, or for a chronographic or chronometric device, and to an associated crystal mounting or removing device.

Watches typically comprise a case which contains the watch operating mechanisms and is closed at its bottom by a cover and at its top by a transparent crystal which allows to view the motion of the hands rotating on the dial.

The transparent crystal, typically made of glass and having a circular perimeter, may be flat or cambered and may further include a gasket for connection thereof with the watch case.

Nevertheless, the crystal may be only removed by opening the case and taking off the movement, as the crystal is typically inserted in the case opening from the inside and has a rim that internally abuts against the case opening edge. As a result, the crystal cannot be removed alone, but requires the watch to be opened and disassembled.

In certain embodiments, the crystal is press-fitted from the outside, without the need to open the watch, but may be only removed from the inside, by disassembling the timepiece, with a high risk of irremediably damaging the crystal, which is associated to a particularly delicate nylon gasket.

The object of the present invention is to obviate the above drawbacks and provide a crystal that may be mounted on a watch and removed therefrom, without requiring any action on the other parts of the watch.

A further object is to provide this as a simple and cost-effective arrangement.

These objects are fully achieved by the inventive crystal and crystal mounting device, which are characterized by the contents of the accompanying claims.

Particularly, the crystal has a thread formed in the thickness of its circumferential edge.

The crystal, that may be made of glass or plastic, may be mounted on a watch case whose inner edge is threaded or on an unthreaded case, which accommodates an adapter ring therein, with an internal thread for connection to the crystal.

The mounting device for screwing the crystal on (or off) includes a preferably cylindrical, manually graspable member, with an operating surface at its bottom, which is shaped complementary to the surface of the crystal and is made of a rubberlike material or of any material that can provide sufficient friction with the crystal when the latter is screwed on (or off).

These and other characteristics will be more apparent from the following description of a preferred embodiment, which is only described by way of example and without limitation in the accompanying drawings, in which:

• Figure 1 is an exploded view showing the crystal, a gasket and the watch case respectively;
• Figure 2 is a view of a mounting device

Referring to the figures, numeral 1 generally designates a watch, whereof the case 2, the dial with hands 3 and a hand position setting crown 4 are shown. The case defines an opening at its top for receiving a crystal 5 and said opening, which has a circular shape, innovatively has an internal thread 2a which is designed to be coupled with a corresponding thread 5a, formed in the thickness of the lateral surface of the crystal 5.

The case opening has an annular abutment surface, not shown, which acts as a support for a gasket 6, adapted to be inserted in the case until it abuts against said annular surface, substantially at the base of the thread 2a.

The crystal 5, which is innovatively threaded, is made of glass or plastic and may have various shapes, substantially flat or cambered, provided it has a circular perimeter, to allow it to be screwed on and off the case 2.

The gasket 6, which forms a mechanical stop member when the crystal 5 is screwed on, also acts as a dust-and waterproof seal, to preserve the tightness of the watch.

In accordance with a variant embodiment, not shown, the case 2 may not be internally threaded, in which case it accommodates an internally threaded adapter ring for connection with the crystal.

The ring preferably also defines an abutment rim or surface for the gasket 6, if this is not already defined by the case.

The invention has been described herein with particular reference to a watch, but may be extended to any chronographic or chronometric device (e.g. a wrist watch, a pocket watch or a table clock, an alarm clock, etc...).

The thread 5a formed in the crystal or the adapter ring advantageously allows an easy and fast replacement of the crystal (which is mounted and removed on the same side of the case opening) without the need of disassembling any other part of the watch.

The crystal may be screwed on and off manually, without using any special tool, nevertheless the Applicant has provided a device 7, which is shown in Figure 2, to facilitate such an operation, which device is substantially composed of a cylindrical member having a bottom surface 8 that is shaped complementary to the crystal 5 and is made of a rubberlike material or of any material capable of providing sufficient friction during the rotary screw on-off motion with the device being manually pressed on the crystal.

On the face opposite the surface 8, the device 7 may have a plurality of pins 9 for interaction with corresponding recesses (not shown) on the back of the case 2, thereby allowing to screw on and off the rear cover of the watch case.

Obviously, crystals having considerably different shapes and cambers will require devices with different surfaces 8, whereby a special mounting device is associated to each crystal type.

The device 7 has a knurl 10 on its lateral surface or, according to an embodiment that is not shown, it may have slide-preventing shapes adapted to facilitate a firm grasp by an operator.