Front brake Girling caliper kit with 3 pistons for 1800 and 122 models manufactured up to 1968.
If you have noticed a surface finish change on the pistons from the old chrome to the new black gas nitriding, here is a summary:
Gas nitriding is a case-hardening process whereby nitrogen is introduced into the surface of a solid ferrous alloy by holding the metal at a suitable temperature in contact with a nitrogenous gas, usually ammonia. The nitriding temperature for all steels is between 495 and 565°C (925 and 1050°F). Principal reasons for nitriding are:
-To obtain high surface hardness.
-To increase wear resistance and antigalling properties.
-To improve fatigue life.
-To improve corrosion resistance.
-To obtain a surface that is resistant to the softening effect of heat at temperatures up to the nitriding temperature.