This system features the S4 4-piston caliper mounted to a 11" 2 piece slot, drill, zinc plated rotor. Baer systems include stainless steel brake hoses as well as calipers that have D.O.T compliant dust and weather seals. Quality SKF or Timken bearings used, along with NAS high grade stainless hardware for our pre-assembled 2-piece rotor. The SS4+ is designed just like Baer's larger systems, but in a smaller package for 15" wheels. This system will come completely pre-assembled on modified stock spindles.