The M6/BN81 Bossard is a type of nut, often referred to as a "blind nut," which is used to attach various components to a threaded hole without access to the opposite side. It's made of aluminum, steel,or brass, and typically features a hex head, flange for stability, and locking collar for greater strength. Some M6/BN81 Bossards feature recessed pockets for use with a hex key, making installation easier in tight spaces.