These rough green (also textured or matte green) Polycord® equivalent endless welded round O-rings have a textured surface that is designed to slip. The rough surface has a low coefficient of friction which is useful in accumulation zones, or where jams happen frequently. Use these O-rings instead of standard clear O-rings when you need the belt to "give" a little, instead of overheating or abrading. The blue versions are food grade polyurethane. Polycord® is a trademark of Habasit AG