- a toothed sector or pinion (15) having a shaft (18) which is rotatably supported by the body of said door closer, said shaft extending with an end portion so as to be keyed to a seat member (43) secured to the floor and to be used as one of the hinge pins upon which the door rotates; wherein the toothing of said pinion is comprised within an angle equal or less than 180°C, and wherein the first tooth and the last tooth (16, 17) of said pinion are of shorter length than the other teeth and are located preferably at the same level;

- a body of annular configuration formed by a pair of similar racks (3, 4) in parallel and opposite relationship receiving said pinion (15) therebetween, the pinion being of such a size as to mesn with either rack with no Sliding movement; said annular body being guided longitudinally in the door closer and being urged longitudinally, in a predetermined direction, by suitable adjustable resilient means (30), the arrangement being such that, with the door closer at rest, the first and the last tooth (16, 17) of the pinion engage the first recesses (44, 45) at one end of each rack, so that the door will be kept firmly and with no backlash in the closed position (so-called 0° position); the teeth of both racks, excepted the last tooth of each rack which is of full length, being of reduced length and being located at a staggered level with respect to the teeth of reduced length of said pinion, so that during the opening of the door, when one rack rolls around the pinion (15) the teeth of the said pinion will not interfere with the teeth of the other rack.