A joint should fail in the bolt, which stretches first, not in the nut threads, which strip suddenly. So a nut's proof stress is set above the strength of its bolt: a 2H heavy hex nut is proof loaded at 175 ksi, against the 125 ksi tensile strength of a B7 stud. ASTM A194 sets the proof stress by grade and style; the load in pounds is that stress times the thread's tensile stress area, so for a 1"-8 2H heavy hex nut it is 175 ksi × 0.606 in², about 106,000 lbf. The nut must carry that load without stripping or breaking, and then come off by hand; a wrench may start it, for no more than half a turn.
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model dataProof stress from ASTM A194 Table 3 (2H heavy hex); mandrel hardness and thread class, loading speed, hold time and acceptance from ASTM A962 and ASTM F606. Tensile stress area from the ASME B1.1 formula; nut drawn to ASME B18.2.2 heavy hex dimensions. B7 tensile strength from ASTM A193 Table 2. The test machine, fixture and grip are generic.
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