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 the highest quality aluminum alloy (2618). To reduce wear, each 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 the MXGP trust in the performance of VERTEX. The VERTEX Top-End Piston Kit saves you time and money since this kit includes everything you need for a piston replacement. The kit includes a piston kit along with a cylinder gasket set and a timing chain. Piston type for 4-stroke: Pro Replica = forged piston corresponds to the original form, Pro HC = forged special piston (higher compression and performance-enhancing).