Due to the increased cylinder pressure in 4-stroke engines, pistons are generally made from forged materials. To withstand the internal pressure of the motor, VERTEX pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston features a MOS2 coating on the piston skirt to reduce wear. VERTEX is an original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in the MXGP rely on VERTEX's performance. The kit includes piston, piston ring(s), wrist pin, and circlips! 4-stroke piston type: Pro Replica = forged piston matching original shape, Pro HC = forged special piston (higher compression and performance enhancing). Enhance your bike's performance with a piston renowned for its durability and reliability, trusted by professionals around the world.