Given the higher cylinder pressure in 4-stroke engines, the pistons are generally manufactured from forged pieces. To withstand the internal pressure of the engine, VERTEX pistons are forged from a high-quality aluminum alloy (2618). To reduce wear, each VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP trust the performance of VERTEX. The kit includes piston, piston ring(s), piston pin, and piston pin lock. 4-stroke piston design: Pro Replica = forged piston corresponds to the original shape, Pro HC = forged special piston (higher compression and performance-enhancing).