Due to the higher cylinder pressure of 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 a premium aluminum alloy (2618). To reduce wear, each VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP also trust VERTEX for their performance needs. The VERTEX Top-End Piston Kit saves you time and money as it includes everything needed for a piston change. Delivery includes: piston kit with cylinder gasket set and timing chain! Piston design for 4-stroke: Pro Replica = Forged piston corresponding to the original shape, Pro HC = Forged special piston (higher compression and performance-enhancing)