PUSH-PINS (barette)

In watchmaking, the push-pin is a cylindrical metal rod with an internal spring that allows the strap to be attached to the lugs of a watch case, as well as to its buckle—whether pin-type (adrillon) or deployant. Both ends are telescopic, pushed outward by the spring, and end in pivots that fit into the holes of the lugs.

Useful link:
Watch case
Bracelets and buckles