One reason we build machinery out of metal instead of brick or glass or wood, is that metals (generally) are ductile as well as elastic, , and work-harden. That is why long thread engagements are stronger than short, in static tension. The early threads deform, so that threads farther down see stress, too, but the threads near the top are still carrying near their yield stress.
But this is not good design practice, because deformation repeats with each dis/re-assembly cycle, with interference between deformed threads further distorting metal. Pretty soon parts won't go together any more, or you observe, "Threads are "stripped"! When did that happen?" They are often not actually stripped, but just chewed out by portions of the male and female threads no longer having matching forms and pitches.
4GSR must be misquoting Shingly, because shear strength of a thread is independent of pitch. Fine threads IN THEORY are stronger because PD and root area are larger. But manufacturing tolerances, and rust, and wear, are more critical because .001" is a bigger % of engagement on a fine than a coarse thread. I stand by my formula, but I will say that "% engagement is a half-assed proxy for the percentage of the theoretical cylinder that is actually there to carry shear.. And threads can fail in flow, and by bursting of the nut.
That is for-why we TEST and use SAFETY FACTORS. Only to God is engineering an exact science, We down here are just fudging about with rules of thumb.
That bolt-doctor website is very good
We're having fun, but OP still has not said what he is building.