[Terry, NJ]

After a lifetime of messing around with bolts, threads, and screws ( I am the only person I know who collects odd size taps) Nominal bolt sizes will mike what ever the size is. Say 1/2X13 will mike .498/499, some will actually mike .500. The tap will mike .505. This why I save broken taps, the shanks are .005 larger than the nominal size. Comes in handy now and then! To make a nut, an undersize hole is drilled. This leaves the "meat" on the nut to cut the thread. The hole or "tap drill" size for a 1/2 " nut is 27/64 or about .421. This will give you a 75% thread. For a greater percentage of thread, simply use smaller tap drills. Ford used a tighter (smaller) hole and a slightly larger bolt size which is why we don't "chase" threads with a tap or die. Chasing threads with today's equipment enlarges them and destroys the original close fit. Although, I do chase bolt threads with an adjustable die opened up most of the way. There now you know more than you ever wanted to know about threads. Terry