Due to 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, these 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 the OEM supplier 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 you time and money as it includes everything needed for a piston replacement. Delivery includes: Piston kit with cylinder gasket set and timing chain! Piston type for 4-stroke: Pro Replica = forged piston conforming to the original shape, Pro HC = forged special piston (higher compression and performance enhancing). Note: Pro Replica Compression 13.5:1, SX(F) 350.