Abstract: Watch case (1) closed by a crystal (3) and a back cover (2) delimiting with a casing ring (6), a space (9) for housing at least a movement (29), including a metal center (30) whose outer wall has a stair structure (31, 31a, 32, 32a, 33) complementary to the inner structure (21, 21a, 22, 22a, 23, 23a) of the cover (20) secured to said center (30) by means of at least two screws (14, 16) passing through it via holes (34, 36) to tighten clamps (15, 17) housed in radial hollows (25, 27) formed in a vertical wall (21a) of the cover (20), by compressing an elastomeric gasket (12) arranged between two horizontal surfaces (22, 32) of the stair structures, and whose thickness is sufficient to arrange clearances (41, 41a) at least between opposite surfaces respectively of the back cover (2) and the base (21) of the cover (20), and the vertical wall (31a) of the center (30) and the wall (21a) of the cover (20) joining the base (21).