>With high strength bolt materials a stress crack is far more likely to >form at the thread. 
 
  Fatigue cracks will always form at the stress concentration. If a bolt fails in fatigue, it will typically fail at the threads or where the head meets the shank. The strength of the bolt material doesn't alter the location of the stress concentration so it doesn't alter the location of the fatigue failure. 
 

Yes Bill the crack will (almost) always form at the thread, or where ever the concentrated stress occurs. We are not talking about long term fatigue here either. I will make this as clear as I can, I WOULD NOT USE A CUT THREAD BOLT ON MY AIRCRAFT PERIOD. The only reason for a cut thread is a situation where the thread pitch is simply not available any other way. One of the factors which has to be mentioned here is thermal expansion. The expansion of the housings will place a lot of additional stress on the bolts or studs. If you wanted to build a test engine that would be used on the ground, OK, no big deal. I can't understand however why anyone would want to build in a failure mode on their aircraft engine! Since bolt/stud failure DOES SOMETIMES HAPPEN NOW in a 13B, with good studs, with rolled threads, I can't understand why anybody would put in a lesser bolt/stud. With the advent of the Internet we can get almost any size or shape bolt within the week from various manufacturers, what is the motivation for a cut bolt other than impatience?