This is a front caliper piston for a Spitfire 1962 to 1967 with two bolt calipers. Two are needed per caliper. The pistons are Plasma Nitrided which will give you the life of Stainless at half the price. The Nitriding becomes a part of the metal and will not flake off or seperate, you can't buy a harder caliper piston. 64325703