Inner Tube 2.75/3.00-21 - Off Road Motorcycle Tire Inner Tube - TR4 Staight Valve Stem - fits on 80/90-21 | 80/100-21 Motorcycle Inner Tube 2.75/3.00-21 TR4 Valve Stem TR4 Valve Stem: Straight Stem, Round Shape to fit on rims with a round valve base. Fits on most 2.75-21, 90/90-21, 80/100-21, 300-21 and others 21" Rim Size Heavy duty durable valve stem. Unbeatable performance and value.