Can the difference between UNC and USS cause a poor fit?

[ericc]

Hi. I needed to make some custom nuts and bolts, so I used an old 5/8-11 die from a set, and a vintage 5/8-11 tap. The nut and bolt fit together, but it was a low quality fit. The more threads meshing, the tighter the fit got. Then, I noticed the letters "USS" on the tap. It's an old one. A web search said they were slightly different from UNC, but still interchangeable. The nut would go on the bolt, but the fit was too tight. Could the difference cause this, or is it more likely just a matter of a worn die. I've always taken thread fit for commercial taps and dies for granted up to now.

 

[matthewsx]

Run the die over it a few more times. Unless you're only putting it together once, then just tighten it down and leave it be.

John

 

[Bi11Hudson]

If it was a lug nut or for a connecting rod big end on a daily driver, I would want the proper fit. If it was for a bicycle frame, run it once and don't worry about it. They are both 60 degree threads, the difference is how "sharp", the final diameter.

.

 

[ericc]

Thanks fellas. I did run the die a couple of times. The bolt, threaded NC, fit a stock nut. The problem was the nut. It is fully suitable for the job, which is as a high current connector. I will just install it and keep my eye out for a new tap.