The bezel (1) is interchangeable via a bayonet device. The shoulder (11) of the middle part (12) is provided with a circular groove (14) and at least two sinks (15) opening out partially into said groove (14). The bezel (1) includes at least two feet (2) positioned to engage in the sinks (15), said feet (2) each including a notch (4) open radially at the emergence of the sinks (15). A locking ring (20) provided with an outer member (21) for rotational manipulation, is positioned in the groove (14), one edge (23) of said ring (20) having a substantially equal thickness to the aperture of the notches (4) and including recesses (24) for the feet (2) to pass and the other edge (25) including a gorge (26) facing a gorge (16) of the middle part (12), the two gorges (16; 26) housing a click spring (30) of the ring (20).