Steel Electro Zinc Plated, Nylon Insulated for Use with Rigid/IMC Conduit. Rugged steel/malleable iron construction. Tapered internal threads for water-tight/dust-tight union. Threads relieved to prevent bottoming of conduit, ensuring sound assembly. Recessed sealing ring at box end; sealing ring captivated. When used with neoprene O-ring, provides watertight threaded hub on enclosures. UL Listed 105°C.