Paul,
Crank bung threads are BSPP 1/4"-19 tpi, (British Standard Pipe
Parallel). I would have thought they would have been tapered, but a
parallel thread tap runs right in without cutting new threads. I guess
that is why the are so well staked.
McMaster-Carr part number: 8328A22, High-Speed Steel Pipe Tap 1/4"-19
Bspp, 2-7/16" Overall Length,
Regards,
Mike Spoelker
Louisville