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 for some of the largest motorcycle manufacturers, and many factory teams in MXGP also rely on the performance of VERTEX. The piston kit includes piston rings, piston pin, and piston pin clips! The 4-stroke piston variant includes Pro Replica = forged piston corresponding to the original shape, and Pro HC = forged special piston (higher compression and performance-enhancing).