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 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 rely on the performance of VERTEX. The delivery includes the piston, piston ring(s), piston pin, and piston pin securing clip. 4-stroke piston design: Pro Replica = forged piston corresponding to the original shape, Pro HC = forged special piston (higher compression and performance-enhancing).