Due to the increased 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). To reduce wear, each VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an OEM for some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on the performance of VERTEX too. The VERTEX Piston Kit comes complete with piston ring(s), piston pin, and piston pin lock! 4-stroke Piston Design: Pro Replica = forged piston matching original shape, Pro HC = forged special piston (higher compression and performance-enhancing).