Bily: Thanks you are correct, the nut did not fully engage ALL the threads on the bolt prior to the stripping of lower threads. The nuts and bolts are galvanized, although now after being stripped, the galvanizing on both the interior of the nut and the bolt are gone.
The reason I suspect the galvanizing portion is stripping is that the upper portion of the thread looks normal, whereas the lower portion of the thread looks shaved. I don't know if this makes it clearer or more confusing.
Also I found John Hassall Inc. doesn't make a 3/4 inch bolt, so this...
Thanks unclesyd. The bolt is marked with a capital "JH" on the bolt head, with "A325" and three equally spaced radial marks. Based on manufacturers I think it may be John Hassall Inc. out of New York.
I'm doing a job using A325 galvanized 3/4 inch diameter bolts for heavy equipment new construction. As required, I've tested them in the bolt tension calibrator and can get only about 14K lbs of tension maximum, before the galvanizing begins stripping off the thread. AISC states that this size...
