A harness gag is a piece of BDSM head gear that is made up of straps, buckles, and attachment points for different kinds of gags, such as ball gags and muzzle gags. The straps are usually made of leather so they won't cut into the skin. The buckles are attached at the back of the head. A harness gag can restrict the movement of the mouth by stretching it open or holding it closed.