Due to the higher cylinder pressure in 4-stroke engines, pistons are generally made from forged parts. To withstand the internal pressure of the engine, VERTEX pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston is equipped with a 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 also trust VERTEX for their performance. The kit includes the piston, piston ring(s), piston pin, and piston pin clip! 4-Stroke piston versions: Pro Replica = forged piston corresponding to original form, Pro HC = forged special piston (higher compression and performance-enhancing)