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 top-quality aluminum alloy (2618). To reduce friction and wear, each VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an original equipment manufacturer (OEM) 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 as it includes everything needed for piston replacement. The kit includes a piston kit, cylinder gasket set, and timing chain! Piston types for 4-stroke: Pro Replica = forged piston corresponds to the original form, Pro HC = forged special piston (higher compression and performance-enhancing).