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Though the info I have doesn't show it, I think those ratings, which are the maximum torque, is for threads at two times the screw diameter. A minimum measurement is generally a thread engagement thickness that is equal to the screw diameter. When I sold for Huck Mfg. years ago, I think that is how they did their tests. I would have to dig out the training tape to watch it again, but if I recall, the maximum torques are for a thread engagement of two times the diameter. A thinner amount of thread engagement, of course, will not hold as much, and is also why you use fine threads on thin materials, instead of course. The chart I have, shows the clamping pressure, for each, at that dry torque, but I didn't include it. They stop it there, as the screw itself starts to yield and stretch, which is normal.
Another thing to remember, is that tap drills in most charts are for 75-80% thread engagement. They use this so the screw or bolt will thread in easily, as one close to 100% will turn tight as it goes in. The chart does not say what percent of threads was measured. I did check this chart with another from Holo-Krome, and it was pretty close. Also, keep in mind that most of these are grade eight fasteners, so a grade two would snap at that torque. This is also why the charts are not generally published, so use common sense, as Clark mentioned, in determining how much torque to apply.
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