Timepiece sub-assembly comprising a component made of micromachinable material comprising an attachment area with a peripheral contact surface, and a shell element deformable between two shapes, one contracted and one expanded, arranged to hold the attachment area inside a housing with at least one degree of freedom, and which comprises a complementary contact surface arranged, in its contracted shape, to exert a clamping force on the contact surface and to securely immobilise the attachment area in all directions, the shell element comprising a first element and a second element that are movable with respect to each other in its expanded shape, each comprising a complementary contact surface, and comprising clamping means for holding the first and second elements clamped together in its contracted shape.