StopTech hard-anodized caliper pistons are available with or without stainless-steel heat shields and in various diameters.
Stainless-steel heat shielded pistons are an upgrade that helps isolate rotor heat from the caliper pistons and ultimately the brake fluid. This helps in long-distance races and allows the driver to use the brakes the same at the end of the race as the beginning.
StopTech calipers regularly have (2) different sized pistons per caliper to ensure even pad wear, so it is important to measure all piston diameters before ordering.