Thomas & Betts 603-TB Electrical Conduit Coupling Brand: Thomas & Betts. Part Number: 603-TB. T&B Conduit Reducer, Threaded, 1 to 3/4 in, For Use With: Rigid/IMC Conduits, Steel, 5/8 in L. Additional Description: TB -603-TB 1 INCH TO.75 INCH THREADED REDUCER. Catalog Description: 1 Inch to 3/4 Inch Reducer, Steel for Use with Rigid/IMC Conduit..