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)...http://www.google.com/patents/US6406178?utm_source=gb-gplus-sharePatent US6406178 - Device for assembling a cover made of hard material on the middle part of a watch
