For 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, the pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston features an MOS2 coating 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 trust in VERTEX's performance. The VERTEX Top-End Piston Kit saves time and money as this set includes everything needed for piston replacement. Delivery includes: piston kit with cylinder gasket set and timing chain! 4-stroke piston design: Pro Replica = forged piston corresponds to original form, Pro HC = forged special piston (higher compression and performance-enhancing)