Due to the higher cylinder pressure in 4-stroke engines, pistons are generally manufactured from forged pieces. To withstand the internal pressure of the engine, VERTEX pistons are forged from the highest quality aluminum alloy (2618). Every 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 also rely on VERTEX's performance. The kit includes a piston with piston ring(s), piston pin, and circlips. The 4-stroke Pro Replica version is a forged piston that matches the original shape, while the Pro HC version is a forged special piston designed for higher compression and enhanced performance.