Clasps, like bosses and corner-pieces, were part of the protective armour of medieval (and post-medieval) bindings. A clasp, either of metal with a hinge, or with an intervening strip of leather or textile, on one board snapped into a catch on the other. Its object was to keep the book closed, relieving any strain on the joints from casual movement. In England and France the clasp was on the upper board, the catch on the lower; elsewhere in Europe the positions were reversed.
Dutch: Slot, klamp