Here's what I would do to estimate the maximum applied torque:
Determine which feature is going to yield first – the thread or the wall section of the threaded feature.
If the thread feature is going to yield first..
Determine the effective thread shear area of the case you're analyzing.
Determine the thread material yield characteristics. -
Using thread shear stress equation – or whatever is most correct determine the applied perpendicular force at the yield strength.
Then, using the generic force vs torque equation, algebraically determine the maximum torque.
Torque related equation and calculators: