MRU chains utilize RK's proprietary Ultra Thin Seal U-Rings which allows the thickness of the seal to be less than 50% of the most common O-ring seal MRU features 4 times longer chain life and will require less chain adjustments than comparable non-sealed 420 chains Lightweight, low friction, sealed, U-Ring 420 pitch chain perfect for Honda« Monkey and Honda« Grom. CHAIN RK BL420MRU X 120