3M Red Heat Shrink Thin-Wall Tubing, 1/2" Inner Diameter, 100 Foot Spool (FP-301-1/2-Red-100')Balances electrical, physical and chemical properties for various industrial and military applications Offers shrink fit protection and strain relief of wires, solder joints, terminals and connections Suitable for lightweight wire harness covering, fire resistant covering, wire marking, wire bundling and component packaging Starts out with an inner diameter of 0. 5 in and after heat is applied it reduces in size to 0. 25 in 100 foot spool 3M(TM) FP