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 an MOS2 coating on the piston skirt to reduce wear. VERTEX is a trusted OEM supplier for some of the largest motorcycle manufacturers; many factory teams in MXGP also rely on VERTEX's performance. The kit includes the piston, piston rings, piston pin, and pin circlips. The 4-stroke PRO HC variant is a special forged piston designed for higher compression and performance enhancement, unlike the Pro Replica which matches the original form.