Due to the higher cylinder pressure in 4-stroke engines, the VERTEX piston is generally made from forged pieces. To withstand the internal pressure of the engine, these pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston is coated with MOS2 on the piston skirt to reduce wear. VERTEX is a supplier to some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust in VERTEX's performance. The VERTEX Top-End Piston Kit saves time and money as this set includes everything needed for a piston replacement. This kit includes a piston set, a cylinder gasket set, and a timing chain! The piston variant for 4-stroke engines: Pro Replica = forged piston corresponds to the original shape, Pro HC = forged special piston (higher compression and performance-enhancing).