Due to the high cylinder pressure in 4-stroke engines, VERTEX pistons are generally made from forged pieces. To withstand the internal pressure of the engine, the pistons are forged from the highest quality aluminum alloy (2618). To reduce wear, every VERTEX piston features a MOS2 coating on the piston skirt. VERTEX is an original equipment manufacturer (OEM) for some of the largest motorcycle manufacturers, and many factory teams in MXGP trust in VERTEX's performance. The VERTEX Top-End Piston Kit saves you time and money, as this set includes everything you need for a piston replacement. Delivery includes: piston kit with cylinder gasket set and timing chain! Piston configuration for 4-stroke: Pro Replica = forged piston matching the original form, Pro HC = forged special piston (higher compression and performance-boosting).