Watertight wrist-watch casing

In a watertight wrist-watch casing including a caseband and an independent bottom removably secured to said caseband by means of screws crossing the bottom and causing a gasket of elastomeric material to be compressed between the caseband and the bottom so as to form a tight seal between these two pieces, the arrangement of a bottom comprising an outer metallic piece and a thin elastomer inner layer lining at least the peripheral part of the inner face of said outer metallic piece to which it strongly adheres by a metal/elastomer junction, said screws pressing a portion of said thin layer against the caseband lower face, wherein said metallic bottom piece has its edges bent upwards so as to come in abutting engagement with the lower caseband face, said thin inner layer having an upwardly projecting rim at its periphery being adjacent to said bent up edges of the metallic bottom piece and extending, when at rest, beyond said bent up edges, the part of said rim so extending beyond said bent up edges being flattened out by the caseband lower face down to the level of said bent up edges, when the casing is closed, the amount of said rim which extends beyond said bent up edges, when at rest, being determined so that closing the casing does not generate in said thin layer a stress exceeding its limit of elasticity.