Due to the higher cylinder pressure in 4-stroke engines, the VERTEX piston is typically made from forged blanks. To withstand the internal pressure of the engine, the 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 for some of the biggest motorcycle brands, and many factory teams in the MXGP trust the performance of VERTEX. The VERTEX Top-End Piston Kit saves you time and money as this set includes everything you need for a piston replacement. Package includes: piston kit with cylinder gasket set and timing chain! Piston version for 4-stroke: Pro Replica = forged piston corresponding to original form, Pro HC = forged special piston (higher compression and performance-enhancing).