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As Tim said, the lubricant used has a large effect on the clamp load (tension in the bolt). Lubricating under the head of the bolt or the face of the nut with a stud has a large effect as well. A dry steel bolt in dry steel has a friction coefficient of 0.3. Oil on both the head and threads brings it down to 0.15 and some moly greases and anti seize compounds can get the friction coefficient down to 0.1. The stress on the bolt or stud for each foot pound of torque torque goes as follows for different lubricants:
Dry 75
Oil 140
Moly 196 Torque and tension is a quirky science. When you dig in deep enough you will find that the best advice is to test your exact assembly and adjust accordingly. What follows is the generic case. The fact that broken head bolts and studs is not a major issue indicates that the book is right and the generic numbers need some adjustment. The stress on the bolt at 55 ft lb will be around 4,000 lb. dry; 8,000 lb. oiled; and 11,000 lb/ moly lube. A grade 5 screw 7/16-14 will yield at a load of 10,200 lb. (Looks like I can't use a link to the Fastenal FASTENER REFERENCE GUIDE on the forum. It should be easy enough to search on the net)
A grade 2 will yield at only 6,200 lb and most stainless steel bolts will yield at 4,000 lb and break at 11,000 (ASTM A193 Grade B8M). The saving grace of stainless steel is that it tends to gall causing the friction to increase under high loads, so they might not break. That is also a conservative estimate and does not take into account the slight work hardening from thread rolling and heading. A grade 8 should start to stretch at 14,000 lb and break around 20,000. (Don't use stainless.) The torque values given in FO-4 for stud nuts appear to be for Grade 5 fasteners. The torque values for studs look like they are for ASTM A354 Grade BC, which is not exactly what I expect to find on the shelf locally.
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