[Jim Sims]

I guess I'd have to say ARP is wrong on this point. There's just no way to totally avoid torsion using a moving screw thread to tension a fastener. A nut's friction generates a traction on the stud's threads at the thread diameter which produces a torque about the centerline. This torque produces a torsional stress in the stud that climbs with the increasing axial tension (which is producing the tensile or clamping stress). Once the nut stops moving the torsional stress (edit gradually) disappears. This condition of combined torsional and axial stress is often the highest a fastener will ever experience which leads to the principle that if a fastener doesn't fail during tightening it isn't likely to fail under it's service tensile stress. Studs can be tightened, and tightened very accurately, with essentially zero torsional stress but it requires a hydraulic stud tensioner which pulls on the stud while the nut is being run down with no load on the nut. I have used such a system combined with a temperature compensated ultrasonic extensiometer to tension hardened 2-1/4" diameter 4140 studs on a 72 ft long rail gun (electromagnetic launcher). Like trying to tension a 72 ft long engine head, talk about fastener cross-talk and tensioning patterns! Cheers, Jim