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


That makes sense, but just brings up more questions....

I understand the fine-threads would give more surface area. But
the thickness - and presumably the holding power - of each
thread would be less, no?

Would there ever be a time that course thread
would be better (other than for cost reasons) ?

I'm still not sure about hardened versus non-hardened. Makes
sense that something more hard might also be more brittle. So
then when would one want hardened? What good is it?

Thanks for the discussion. I'm not too worried about my choices
in this case because the whole bolt thing is just temporary until we
weld the chains on. (We'll leave the bolt too). But as an opportunity
to learn something it's interesting.