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). Each VERTEX piston features an MOS2 coating on the piston skirt to reduce wear. VERTEX is an OEM supplier to some of the largest motorcycle manufacturers, and many factory teams in MXGP trust the performance of VERTEX. With the VERTEX Top-End Piston Kit, you save time and money, as this set includes everything you need for the piston replacement. Delivery includes: piston kit, cylinder gasket set, and timing chain! Piston design for 4-stroke: Pro Replica = forged piston corresponds to original form, Pro HC = forged special piston (higher compression and performance-enhancing).