Due to the higher cylinder pressure in 4-stroke engines, the piston is 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 and tear. VERTEX is the original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust the performance of VERTEX. This piston kit includes the piston, piston ring(s), piston pin, and piston pin clips. The 4-stroke piston versions available are Pro Replica, a forged piston that corresponds to the original shape, and Pro HC, a high compression forged specialty piston designed for enhanced performance.