Gary Warner wrote:
Finally, a thread about threads.

Silly question but just for discussion sake: I am bolting some safety chains
to our home-made trailer. Eventually they will be weled on as well as bolted
but for now (long story) we just want to bolt them.

So I got a 4" bolt in "Grade 8" hardened steel. But they come in both
course and fine thread. I went for the course thread. Question: Is there
any functional difference or reason to choose a course versus a fine
thread for this type (or other) applications??

But of course. Why else would there be so many different threads?

You want fine thread. The engagement, or amount of material 'gripping'
between bolt & stud, will be approx twice as much. Stronger and less
tendency to vibrate loose.

BTW hardened steel may not have been the best choice either. High
hardness usually corresponds to more brittle. It may just be surface
hardened which wouldn't make a huge difference.

Fresh Breezes- Doug King