Due to the higher cylinder pressure of 4-stroke engines, the VERTEX piston is generally made from forged pieces. These pistons are forged from the highest quality aluminum alloy (2618) to withstand the internal pressure of the engine. To reduce wear, each VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is the original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on VERTEX's performance. The VERTEX Top-End Piston Kit saves time and money because this set includes everything needed for the piston replacement. The kit includes the piston, cylinder gasket set, and timing chain! Piston Design for 4-Stroke: Pro Replica = forged piston matching the original form, Pro HC = forged special piston (higher compression and performance-enhancing).