Originally Posted by flick  I'm going on memory here, so correct me if I'm wrong:.... |
I think you are correct. It is just if you are making a large coarse thread the flat will look quite wide at 75%. I would do this for an in-house job but for a customer I would be more cautious; if the customer questions it you do not in fact have it exactly to spec.
Another reason for using 75% is because practically all the tap drill charts use this; no memory needed.
