Rack Angle Adapter Brackets mount to ProLine and ProLine G2 Rack Angles. They bring out the rear leg mounting surface to allow traditional Rack Mount Slides (A16SL2U, sold separately) to be used. Fits tapped or through-hole ProLine and ProLine G2 Rack Angles. Rack Angle Adapter Brackets come in a quantity of four and are 14 gauge steel. They have a plated finish.