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 a MOS2 coating on the piston skirt to reduce wear. VERTEX is an OEM supplier for some of the largest motorcycle manufacturers, and many factory teams in MXGP trust VERTEX's performance. The kit includes a piston, piston ring(s), piston pin, and piston pin lock! 4-stroke piston versions include Pro Replica, a forged piston in the original shape, and Pro HC, a forged special piston with higher compression and performance enhancement.