The MotoSport.com Pro-X Piston Kit - 4-Stroke includes one of each of the following components with the following attributes: Pro-X Piston: Important note: This piston is for a stock sized bore. Please measure your cylinder to check clearance before ordering. ProX pistons are precision machined on the latest, state of the art CNC equipment. The same low-expansion, low-friction piston alloy is used as is used for all major Japanese and European engine manufacturers. ProX Piston Kits are a first class solution to replace the original piston in your machine. Most ProX pistons come with a coating. The O.E.M. style tin-coated pistons assist the wear-in process as when you first started the bike. ProX has developed a new skirt coating that not only assists the wear-in process, but also helps reducing friction after the wear-in. The black coating is made from a delicate mix of materials and will increase performance.