This is an original Seiko ratcheting clasp that can be placed in bracelets that are 18mm wide at the at the clasp, using two push pins. It is only available in 18mm.. This ultimate divers’ clasp has 13! positions and adds more than 3cm to the length of your bracelet. This clasp can also be used with rubber straps that have a metal clasp (those you have to cut to size), like the MM300 strap from Crafter Blue.