Replaces stock piston on 2 valve engines with 49.5mm stroke (86cc – 107cc) or 2 valve engines with 52.4X57mm bore and stroke (124cc). Must have 13mm Piston pin. Some popular 124cc models that can benefit from this piston are the Pitster Pro GPX, Extreme, UPC, and Thumpstar. Piston kit comes complete with rings, circlips, wrist pin, and piston. Compression ratio on this kit is 12.5:1 over the stock ratio of 9:1. Uses your stock type gaskets.