T.R. McElroy's Mac Key Morse Code Telegraph Key - Serial Number 5650 A Morse code paddle telegraph key from the 1930s on 4" x 5 7/8" cast iron base, with brass identification plate T.R. McElroy's Mac Key Pat. Appl'd For with serial number 5650. The underside of the base is cast with SEMI-AUMC TGH & RDO CODE XTR MAC 9-34 KEY MFD AJD & GA BY T R McELROY WLDS FASTEST RDO TGHR BOSTON MASS, short for Semi-Automatic Telegraph and Radio Code Transmitter Mac Key Manufactured Adjusted and Guaranteed By T.R. McElroy Worlds Fastest Radio Telegrapher Boston Massachusetts. The key shows moderate signs of age with varying signs of rust to all parts, scratches to the chrome, and the plastic base feet show cracks. See photos for best description.