Due to the increased cylinder pressure in 4-stroke engines, the pistons are generally made from forged pieces. To withstand the internal pressure of the engine, VERTEX 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 rely on VERTEX for their performance needs. The piston kit includes piston rings, piston pin, and piston pin circlip. The 4-stroke piston variants: Pro Replica = forged piston corresponds to the original shape, Pro HC = forged special piston (higher compression and performance enhancing).