This system features the 4-piston, S4 caliper mounted to a 13", 2 piece slot, drill, zinc-plated rotor. The S4 caliper has D.O.T compliant dust and weather seals and uses the popular DR1-C pad type. Rotors are pre-assembled with NAS high grade stainless hardware. Baer’s unique backing plate not only acts as a caliper mount, but also houses a modern 1-piece park brake shoe assembly. Stainless braided hoses and hardware are also included. The 13" SS4+ fits most 17” or larger wheels. Fits 1971-76 GM Full Size Passenger Cars w/OE Large Pattern 10/12 Bolt Bearing on Axle (BOA) Housing Ends