The higher cylinder pressure in 4-stroke engines necessitates that VERTEX pistons are generally forged. To withstand the internal pressure of the engine, these pistons are crafted from the highest quality aluminum alloy (2618). Each VERTEX piston features a MOS2 coating on the piston skirt to reduce wear. VERTEX supplies some of the largest motorcycle manufacturers with original equipment, 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 needed for a piston replacement. The kit includes a piston, cylinder gasket set, and timing chain! Piston design for 4-stroke: Pro Replica = forged piston corresponding to the original form, Pro HC = forged special piston (higher compression and performance-boosting).