Inner Tube - Standard - 12" - TR-4 - Center Metal Valve " butyl tubes" made from butyl polymer, unlike other "butyl" tubes, which are blended butyl polymer and natural rubber, Each tube is individually boxed with a full range of sizes and valve stem types clearly marked on each box end, butyl tubes minimize natural air leakage and maintains air pressure for longer period of time, All stems are TR-4 type for valve stem