This is something every owner of an older Burroughs calculator or adding machine will want.
The Burroughs company did not want users to poke around the internals of their adding machines. To discourage such 'tinkering', the cases were locked and needed a 'B-key' to unlock. It's possible to jimmy the lock (a thin blade between base and cover to push the latch away) or sometimes just lots of jiggling to get the cover off - but with a B-key it becomes so much easier :-)
The dimensions of these keys are fortunately findable in the hive-library that is the internet.
Rummaging in the collection of old-keys, a little key with hollow shaft and an outside diameter of just under 5mm was found. This was then filed/sawed to create the pronged B-Key; the dimensions aren't too critical - the prongs just have to fit in the cut-outs of the latch. The inside diameter of the shaft does need to be large enough to fit around the central stem in the lock of course, so drilled out to 3.2 mm.
Result; a newly minted B-key.