Definition - What does Harness Gag mean?
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.
Kinkly explains Harness Gag
A harness gag is used in bondage play. For the wearer, it creates a feeling of helplessness and objectification. Some of these gears are made to restrict vision and hearing, which adds to the helpless feeling. A harness gag is meant to restrict movement, not necessarily to cause pain. Make sure the wearer is comfortable, and the straps are not too tight against the skin.