This is a La Ceinture de Chastete collar. The collar is made from stainless steel strapping with a high polish. The interesting thing is the lock mechanism. A stud welded into one goes through a hole in the other end. The stud itself has a through hole. The cap piece carries a lock with a pin coming out of its body. The cap is placed over the stud, and when the lock is shut around the cap, the locking pin in the body of the lock fits into the stud, locking on the cap and collar.