Well, you can skip the theory and measure this, w/ a cupla calc's.
Fasten a tight-fitting washer, 1" OD, to resist the delrin as the bolt/delrin are tightened. Hold/turn whatever/however is most convenient, and turn w/ a wrench/pipe of known length, w/ some estimable applied force, to the stripping point. Use r1F1 = r2F2. Multiply F2 by (20*12) (the pitch and foot conversion), to get the force due to the mechanical advantage of the thread pitch. r1, F1 are the applied radius/force of the wrench, and r2 is that of the bolt, somewhere between the major/minor radius of the bolt.
If the whole thickness of the delrin can't be used, use whatever thickness is practical, and extrapolate linearly to the full thickness, as this should be linear.