M1790, 250W, 250V, 3 Way, Incandescent Metal Shell Lampholder, Medium Base, Single Circuit, Caps threaded 1/8"-27 I.P.S. Fit standard lamp stems, Set screw prevents rotation of socket, Aluminum brass dipped finish, Two circuit (3 way) sockets operate dual filament lamps on sequence of low, medium, high, off, UL Listed, SA, Bulk.