TAC "Hole in the Wall" made by one of T.R.McElroy's companies "TELEGRAPH APPARATUS CO. NOT INC. CHICAGO,ILL.USA" ca 1944-1946
The "hole in the wall" type came as the model 510 (standard, painted base) and the model 810 (deluxe, with chrome base).
The nickname "Hole in the Wall" comes from the square frame with a round hole
in the middle for the lever to pass through. The CP-510/810 series uses the widest base you’ll find on a bug — a full 4 inches.