Due to the higher cylinder pressure in 4-stroke engines, VERTEX pistons are generally manufactured from forged pieces. To withstand the internal pressure of the engine, the pistons are forged from high-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 also trust VERTEX's performance. The VERTEX Top End Piston Kit saves you time and money because this set includes everything you need for the piston replacement. Delivery includes: Piston kit with cylinder gasket set and timing chain! Piston design for 4-stroke: Pro Replica = forged piston corresponds to original form, Pro HC = forged special piston (higher compression and power-boosting design).