Due to the higher cylinder pressure in 4-stroke engines, the piston is generally made from forged pieces. To withstand the internal pressure of the engine, VERTEX pistons are forged from high-quality aluminum alloy (2618). To reduce wear, each VERTEX piston features an MOS2 coating on the piston skirt. VERTEX is an OEM for some of the largest motorcycle manufacturers and a trusted name in MXGP, with many factory teams relying on VERTEX performance. The package includes the piston, piston ring(s), piston pin, and piston pin retainers! 4-Stroke Piston Versions: Pro Replica = forged piston corresponds to the original form, Pro HC = forged special piston (higher compression and performance-enhancing)