Due to the higher cylinder pressure in 4-stroke engines, pistons are generally made from forged pieces. To withstand the internal pressure of the engine, VERTEX pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston features an MOS2 coating on the piston skirt to reduce wear. VERTEX is the original equipment manufacturer for some of the largest motorcycle brands, and many factory teams in MXGP trust in VERTEX's performance. The kit includes a piston, piston ring(s), piston pin, and circlip! 4-stroke piston variants include Pro Replica, which is a forged piston matching the original shape, and Pro HC, which is a forged special piston offering higher compression and increased performance.