BC4340CPSS (OD = 43.00mm / Length = 40.00mm) ---------------Each polished 316L stainless steel 'Lifetime' piston is to replace damaged or corroded OEM caliper pistons. Type 316L is an austenitic chromium-nickel stainless steel containing molybdenum. This increases corrosion resistance, improves resistance to pitting from chloride ion solutions and provides increased strength at elevated temperatures. Type 316L is one of the highest specification stainless steels available - superior to both 303 & 304 grade stainless steel.