Due to the higher cylinder pressure of 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 an 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 piston with piston ring(s), piston pin, and piston pin lock! 4-stroke Piston Version: Pro Replica = forged piston matching the original form, Pro HC = forged specialty piston (higher compression and performance enhancing).