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 motor, the pistons are forged from the highest quality aluminum alloy (2618). To reduce wear, every VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an OEM supplier for some of the largest motorcycle manufacturers, and many factory teams in MXGP also 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. This kit includes the piston kit along with a cylinder gasket set and timing chain. Piston Design for 4-Stroke: Pro Replica = forged piston corresponds to the original shape, Pro HC = forged special piston (higher compression and performance-enhancing).