Due to the higher cylinder pressure of 4-stroke engines, the VERTEX piston is generally crafted from forgings. To withstand the internal pressure of the engine, these 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 an original equipment manufacturer (OEM) for some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust VERTEX for its performance. The VERTEX Top-End Piston Kit saves you time and money, as it includes everything needed for the piston replacement. Delivery includes: Piston kit with cylinder gasket set and timing chain! Piston type for 4-stroke engines: Pro Replica = forged piston matching original shape, Pro HC = forged special piston (higher compression and performance enhancing).