This insulator was the Locke #311 first cataloged in 1903 when a series of these three part mushroom shaped multiparts were introduced. Brookfield, Elmer glass, Columbia, Jumbo, Locke glass, Fred Locke J-M trolley), Mayer & Englund (glass, Imperial, New Lexington), McCarthy Bros. & Ford (SP, Hemingray, West. M-3060 specimens known with Fred Locke markings have come from only one source a Hemingray, tubes, knobs, cleats), Hendrie & Bolthoff Mfg & Supply (SP, Hemingray, Locke), Hendrix Wire & Cable Corp. (polyethylene styles), Henry L. Walker Co. (SP, nail-knobs, cleats, S-H Co. tubes, wood P&S, railway, Locke pins, Locke glass, Locke porcelain, Brookfield, OT-60 Oil Insulation Dielectric Tester Manual. Ohio Brass (H-T Porcelain Insulators) - Jan. Ohio Brass Co. (April - Elec., Rail & Mine) - (Hemingray), Ohio Brass (Elec Rrwys, Mine, Trans.) Vintage ad for Hemingray Glass Company. Like the M-2430, which was first introduced by Fred ), Corning Glass Works (radio ins) -- 1994 Houston Nat. M-2220B (Locke catalog #101) Production date:1903-04 M-2220B.