The increased cylinder pressure of 4-stroke engines necessitates the use of forged pistons. These VERTEX pistons are crafted from the highest-quality 2618 aluminum alloy to withstand the internal pressures of the engine. 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 and is relied upon by many factory teams in the MXGP for its performance. Every piston kit includes piston rings, piston pin, and circlip! For 4-stroke applications: the Pro Replica is a forged piston that matches the original form, while the Pro HC is a forged specialty piston offering higher compression and performance enhancement.