Stainless steel "S" caliper piston for calipers that take 7.5"wide brake disc as used on all Cooper "S"variants and early 1275GT. These are correctly ground for long life and fitment against the seals, but nore importantly have the raised crown section on the area to allow the fluid to correctly push the piston out. Made in stainless steel to reduce heat transfer to caliper fluid and for longevity.