Given the higher cylinder pressure of 4-stroke engines, VERTEX pistons are generally made from forged materials. 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 an original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on VERTEX's performance. The VERTEX Top-End Piston Kit saves you time and money, as this set includes everything you need for a piston replacement. The kit comes with a cylinder gasket set and a timing chain! The 4-stroke piston variant: Pro Replica = forged piston corresponds to the original form, Pro HC = forged special piston with higher compression and performance enhancement.