When it comes to safety critical parts, only fit the original suppliers' parts as repair kits. The kit includes all the seals needed to do 4 pistons in one caliper. If you are fortunate enough to have 4 pot calipers from the Turbo/Metro on your Mini, then there will come a day when you need these rebuild kits. The piston design is great for stopping, but higher in maintenance cost. All turbo vented disc calipers use these "A" kits, plus all the later type Metro non vented disc calipers. Sold individually per caliper.