Due to the higher cylinder pressure in 4-stroke engines, 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 is equipped with a MOS2 coating on the piston skirt. VERTEX is the original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust the performance of VERTEX. Delivery includes piston, piston rings, piston pin, and circlips! Piston type for 4-stroke: Pro Replica = forged piston corresponds to the original shape, Pro HC = forged special piston (increased compression and performance enhancement).