Due to the higher cylinder pressure of 4-stroke engines, pistons are generally made from forged parts. 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 for some of the largest motorcycle manufacturers. Many factory teams in the MXGP also trust VERTEX for their performance needs. This kit includes the piston, piston ring(s), piston pin, and piston pin clips. The 4-stroke piston variants are available in Pro Replica (forged pistons matching the original form) and Pro HC (forged special pistons with higher compression and performance enhancement).