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 an MOS2 coating on the piston skirt to reduce wear. 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. The kit includes a piston, piston ring(s), piston pin, and piston pin circlip. The 4-stroke piston versions are: Pro Replica = forged piston corresponding to the original shape, Pro HC = forged special piston (higher compression and performance-enhancing).