Abstract: The casing comprises a body and two glasses one of which plays the role of the bottom. These two glasses are pressed against the body by eight clamps having the shape of stirrups overlapping the horns of the attachment elements of the wristlet. Each pair of clamps is traversed by two screws, one engaged from above, the other one engaged from underneath ensuring the tightening. Clamps are provided with shoulders by means of which they bear on bevels on the two glasses.