See more: Pistons & Piston Rings
Fits KB 300 series 3 13/16" Big Bore pistons for Evolution Big Twin, For standard thru +.030" bore
A limited number of KB pistons have the ring grooves crossing the piston pin hole. In order to have the piston rings properly supported these pistons come with piston ring support rings. As support rings do not have a sealing function they do not have to be replaced when you install new piston rings, but sometimes new ones are needed because a ring is lost or broken.