Due to the higher cylinder pressure in 4-stroke engines, VERTEX pistons are generally made from forged pieces. In order to withstand the internal pressure of the engine, the pistons are forged from the highest quality aluminum alloy (2618). To reduce wear and tear, every VERTEX piston has 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 rely on VERTEX 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 type: 4-Stroke Pro Replica = forged piston corresponds to the original shape, Pro HC = forged special piston (higher compression and performance-enhancing).