The VERTEX Piston Kit for Kawasaki Pro Replica is crafted to endure the higher cylinder pressure of 4-stroke engines, 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 is coated with MOS2 on the piston skirt to reduce wear. VERTEX is the original equipment manufacturer for some of the largest motorcycle manufacturers, and many factory teams in MXGP rely on the performance of VERTEX. The package includes the piston, piston ring(s), piston pin, and piston pin retainer! The 4-stroke piston design: Pro Replica = forged piston matching the original form, Pro HC = forged special piston (higher compression and performance-enhancing), Note: Compression 12.5:1 (2013-2014)