This system features the S4 4-piston caliper mounted to a 12", 1 piece slot, drill, zinc plated rotor. The S4 caliper has D.O.T compliant dust and weather seals and uses the popular DR1 or HB100 pad type. 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 are also included. The 12” SS4 fits most 16” or larger wheels. Fits 1971-76 GM Full Size Passenger Cars w/OE Large Pattern 10/12 Bolt Bearing on Axle (BOA) Housing Ends