Your picture brought to mind a BD drill that I have. I don't have any pictures at this point, but I can share the information that is on my plate. My serial number also starts with a letter, it is Z4781. Now I can't tell you how old this drill is but the plate has is as a type Z (the letter in the serial number is the same is the type of drill. Type may be the same a model). The size is 5/16 and draws 1.7 amps. The patent date is November 8, 1917. The difference with mine to yours is it has a cover plate (missing) on the rear of the handle. I think it is for access to the switch (also missing).
I got the drill maybe 15 years ago from my wife uncle. Other than that I know noting about the drill. Oh, it does not have a standard chuck it is a 2 jaw.
Last edited by Fastback; 10-27-2012 at 08:02 PM.