Due to the higher cylinder pressure in 4-stroke engines, pistons are generally made from forged pieces. To withstand the internal pressure of the engine, VERTEX pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston features a MOS2 coating on the piston skirt to reduce wear. VERTEX is an original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust the performance of VERTEX. The kit includes the piston with piston ring(s), piston pin, and piston pin lock! 4-Stroke Piston Design: Pro Replica = forged piston matching the original shape, Pro HC = specialty forged piston (higher compression and performance-enhancing)