Intermediate Metal Conduit (IMC) was developed in the 1970s as a thin-wall alternative to rigid steel conduit (RSC) that weighs about one-third less. IMC ships with either a straight-tapped or integral coupling. It features a galvanized OD and ID.
IMC is covered under Article 342 of the NEC, UL 1242 and ANSI C80.6.
IMC is interchangeable with galvanized RMC. Both have threads with a 3/4-inch-per-foot taper, use the same couplings and fittings, have the same support requirements and are permitted to be used in the same locations