So if you look at torque charts for a particular type of fastener, those charts have torque value for a particular size and particular steel tensile strength, etc. The charts should have the basic information about where the torque value comes from, such as 75% torque to yield, lubrication, etc. So if you know you have a 170ksi cap screw, and the chart is for a 170ksi cap screw, it will give you the suggested torque (based on 75% of yield, lubricated, etc) that is safe for that screw. That's a good starting point for the fastener, without doing an involved bolted joint analysis.
The 2024 plate is more involved, as there are usually some thread shear stress calculations to find out what it will actually hold, and of course this also changes if there is a threaded insert, etc. There are threaded hole charts for different materials that will give tapped hole strength based on depth to diameter, etc.. You're a machinist, so you already know that using a Heli-Coil or similar insert will increase strength as well.
I think you need to back up and think about what clamping problem you're trying to solve here though; are you having problems with something leaking because you're losing clamp load, or having problems with cyclic fatigue, or with fastener pullout, those sorts of things....
Bolted joint design usually starts with a clamp load analysis, to find out what strength you need for the application. Then you find out how to get there based on fastener size, quantity, tensile strength, torque, etc.
Am I that predictable...?
