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). To reduce wear, each VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an OEM supplier to some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust the performance of VERTEX. The piston is delivered including piston ring(s), piston pin, and piston pin lock! Piston design for 4-stroke: Pro Replica = forged piston corresponding to the original form, Pro HC = forged special piston (higher compression and power-increasing). Upgrade your motorcycle's performance with our VERTEX Piston Kit that ensures durability and excellence under high pressure conditions.