"Esourcedesigns" wrote in message
...
A fine thread bolt or nut does NOT give you additional surface area to
grip.
The cut depth of the bolt threads is less for a fine thread bolt than it
is for
a course thread, but due to the number of threads the surface area is
almost
identical. Fine threaded bolts are used most often in high clamping force
applications because it offers less drag when torgued therefore applying
more
force to the item being clamped. A fine thread bolt is no less or no more
prone to vibration failure than a course thread. A fine thread bolt
merely has
to turn a greater number of times to fall out. Either way it is easily
remedied with the use of a thread locking compund or a simple lock washer.
A
grade 8 bolt could never be considered brittle. Grade 8 bolts are used in
automotive main and rod cap applications and are less likely to strech
under
high torque than a lesser grade. By the way 9 out of 10 bolt and nut
failures
are not due to the thread but to the shank of the bolt streching,
weakening
then failing.

A grade 8 bolt is made from grade 8 steel and it is not a surface
hardening.
The same is for a grade 5. A grade 3 bolt, a bolt without markings, can
be
made of any material less than a grade 5. Some grade 3 bolts will fail
under
only slight pressure while others will hold under greater.

If you don't know what you're talking about leave the matter to someone
who
does.

Dennis
ASE Master Auto Technician and
Marine Engineer in training

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


Grade 8 is not always a good choice for clamping two things together. You
have to have the two items with enough strength to stretch the bolt when
clamping them. Main and rod caps suffice. To keep the bolt from loosening,
you have to stretch it enough in the elastic region that any vibration
causing varying forces on the bolt that the bolt does not go out of the
elastic region. Clamping a chain, probably does not allow a grade 8 bolt to
stretch enough. You may be better off with a grade 5 bolt, and most safety
chains are probably not even bolted with that high of grade bolt. Figure
that for years, a wimpy S hook was the safety attachment to the vehicle. And
I doubt the S hook is grade 5. At least in California, a simple S hook has
to have a retainer to keep it from bouncing off the hitch. A rubber snubber
will work. I use a screw together link. Senior moment as to the name. A
carbiner clip would also work.