With 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). Each VERTEX piston features a MOS2 coating on the piston skirt to reduce wear. VERTEX is an OEM for some of the largest motorcycle manufacturers, and many factory teams in MXGP trust VERTEX for performance. The kit includes the piston along with piston ring(s), piston pin, and circlips. Piston design 4-stroke: Pro Replica = forged piston corresponds to original form, Pro HC = forged special piston (higher compression and performance-enhancing).