Regular saddle pads can cut off blood supply to the withers when they are pulled down taut. The cut-out prevents pressure from being applied onto that area and slightly lifts the saddle away from the withers. The Halfpad with Wither Relief is cut to fit Dressage, Close Contact and All Purpose saddles equally well and can be worn by itself, over or under a thin square pad. Small - Close Contact Saddles 16” and 16.5” Regular - Dressage, Close Contact, All Purpose saddles 16.5” - 18”