The Marrette ACS aluminum wiring wire connector is a fixed spring, twist-on connector made of special spring wire materials and coatings to meet the rigorous standards for aluminum wire connections. Made of sturdy, thermoplastic valox resin 257 deg F rated Deep, wide throat ensures full insulation coverage Threaded entry helps guide large wire bundles right into the spring Made of a special bronze alloy and then plated with a thick coating of tin to satisfy the rigorous standards established for aluminum wire connections Round spring design ensures that aluminum conductors and highly stranded copper wires are not scored or severed when joined