Given the increased 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. VERTEX is an OEM supplier to some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on the performance of VERTEX. The piston is delivered including piston ring(s), piston pin, and piston pin lock ring! 4-Stroke piston type: Pro Replica = forged piston matches the original form, Pro HC = forged special piston (higher compression and performance-enhancing).