For whatever it's worth the standard form of a US thread is not a sharp V. The normal form of a 60 US thread has the crest of the external thread flattened by 1/8H (H= height of the theoretical sharp V) & that of the internal thread flattened by H. The normal "Tap" drill size or the normal pitch diameter for the external thread will ensure that neither ends up as sharp V.
Though somewhat dated now I have a set of thread spec book which I had to acquire when going through my machinist apprenticeship back in the 1960's.
If anyone has a specific thread they would like more info on let me know & I will look & see if it is covered. They do cover several British threads (including Whitworth) as well as metric & many unusual US threads even including light bulb threads.
Although not "Exact" a working solution for a tap drill for a 60 thread is to subtract one pitch length from the nominal diameter & then use the closet drill size possible. This will apply to either metric or US pitches, but remember that with US threads being given a TPI the pitch length is 1/TPI. Thus for instance a -20 thread would have a pitch length of 1/20 or 050". A workable tap drill would thus be 200".
