I have done a Calculation for a hook that is attached to a lower block with threads on the shank and a nut on those threads. After performing the Normal/Static stresses, I took a look at the fatigue stresses. On page 387 of Peterson's Stress Concentration Factors, 2nd Edition (and similarly on page 253 of Peterson's Stress Concentration Factors - 1974) there is a discussion on 'Bolt and Nut' stress concentrations.

Anyhow, it states that Hetenyi determined that a factor of 2.7 could be used on a standard nut/bolt. This is the value I used and I believe to be sufficient for determining fatigue stress. However, the Customer pointed out that it continues on to say that Brown and Hickson determined that a factor of 6.7 should be used. There is a lot of conflicting discussion in this Section as it continues on.

I was hoping that somebody may have insight into this situation and could enlighten me.

Thanks for your time.