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Steel fasteners do not need reduced torque for 1/2 nuts. The torque values in charts from reputable bolt suppliers like Fastenal are based upon the allowable torsional strength of the bolt material. As long as the nut is the same grade as the bolt even a half nut will fail the bolt first. Beware of using nuts from the hardware store however; you have no way of knowing what grade they are [no markings like bolts]. For internal threads in softer materials you need to worry about thread engagement length unless it is just a jam nut like on a radius rod or tie rod. You'll notice that head bolts for iron blocks and aluminum blocks have different lengths [longer threads for aluminum.]
Considering how lethal a failed fastener can be I wish racers would better educate themselves on this subject. The more you know the better you'll monitor your race car's hardware and probably change them more often.
The very best book on this subject for racers is Caroll Smith's on Nuts & Bolts. The exact title escapes me but it is available through Steve Smith Motorsports. It is part of his Engineer to Win, Tune to Win, Prepare to Win series. He joked that they wouldn't let him use "Screw to Win."
I was shocked to find GRADE 2 bolts in the "complete sprint car bolt kit" sold by a national speed shop. Poor Caroll Smith must be turning in his grave. Rule #1 from him was "Grade 5 minimum"!
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