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 (OEM) for some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on VERTEX's performance. The piston kit includes piston ring(s), piston pin, and piston pin clips. 4-stroke piston types: Pro Replica = forged piston matching original form, Pro HC = forged special piston (higher compression and performance-enhancing)