Due to the higher cylinder pressure of 4-stroke engines, the piston is 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 a trusted original equipment manufacturer for some of the largest motorcycle companies. Many factory teams in the MXGP also rely on the performance of VERTEX. The piston kit includes piston ring(s), piston pin, and piston pin circlip. The 4-stroke piston version: Pro Replica = forged piston corresponds to the original form, Pro HC = forged special piston (higher compression and performance enhancing). This advanced piston kit is designed to offer improved engine efficiency and longevity, providing top-tier performance for competitive and recreational riders alike.