Namura NA-50000-4 .040 Piston Kit for Polaris 250 Namura pistons are made to exact OEM specifications and are direct replacements for OEM pistons with no modifications or dimensional adjustments needed Piston kits come with the piston(s) individually wrapped, a set of OEM quality rings packed in their own box, wrist pin(s), and circlips Namura pistons have MOS2 (Molybdenum/Teflon) skirt coatings, high-silicon aluminum and anodized domes A, B and C pistons are available to help extend the life of expensive Nikasil, SCEM, Boron Composite and Ceramic Cylinders Namura rings are made by Riken, the world's largest OEM manufacturer and are the same OEM rings used on more motorcycles and ATV's than any other brand