Rear Brake Caliper Piston Kit. The All Balls Racing Rear Brake Caliper Piston Kit is an aftermarket replacement kit designed to fully upgrade or replace a corroded, damaged, or sticking rear brake caliper piston on motorcycles, ATVs, and UTVs. The replacement pistons are precision-machined from high-grade 304 stainless steel. Stainless steel reduces thermal conductivity into your brake fluid by up to 93% compared to standard aluminum pistons, helping prevent brake fade. Unlike O.E.M. chrome-plated steel or aluminum pistons, these stainless steel components will not rust, pit, or become brittle with age. Each packaged part number contains the piston (or pistons) required to fully rebuild exactly one rear caliper. Note: Kit contents will vary depending on model and may not match image shown. Kit Includes: 1 caliper piston(s).