Due to the higher cylinder pressure of 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 original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on VERTEX's performance. The piston kit includes piston rings, piston pin, and circlips. The 4-stroke piston design Pro Replica is a forged piston that corresponds to the original form, while the Pro HC is a forged special piston (higher compression and performance-enhancing).