The increased cylinder pressure in 4-stroke engines typically requires pistons to be made from forged materials. VERTEX pistons are forged from the highest quality aluminum alloy (2618) to withstand the internal pressures of the engine. Each VERTEX piston is coated with MOS2 on the piston skirt to reduce wear. VERTEX is a trusted original equipment manufacturer for some of the largest motorcycle manufacturers. Many factory teams in the MXGP also rely on the performance of VERTEX. The kit includes the piston, piston ring(s), piston pin, and piston pin circlip! The Pro Replica model is a forged piston that matches the original form, while the Pro HC model is a forged special piston designed for higher compression and enhanced performance.