The drill chart specifies a 23/32" bit for a 1/2 NPT plug. Yet, 23/32" = .718...still less than the .75" hole. When I place a 1/2 plug next to, or try to thread it into the hole - it is oversize to the 3/4" hole. So... it might be best to just try using the 1/2 NPT tap, tap it as is, and see how the plug will fit.
Seems like my best option...other than enlarging the hole to fit a 3/4 plug (last resort) (57/64" drill = .89 hole) or, try to fit a threaded bolt into the hole and use a nut, fender washer, and gasket to seal the hole without tapping. However, there is no room inside the block for the hex head of a bolt to fit due to the location of the hole near the interior front of the block.
Seems like a simple thing - but I'll tell ya, with my lack of experience, these simple things require a steep climb on the learning curve...
Last edited by tom moore; 10/28/2019 5:45 PM.
