Fine Thread vs Course Thread
 

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??

Fine Thread vs Course Thread
 

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

Fine Thread vs Course Thread
 

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.

Fine Thread vs Course Thread
 

Fine thread bolts are usually torqued 9% more than course threads, for whatever
that is worth. A harder bolt is stronger in "shear" or torsion but not in an
application where it is going to be bent. Your bolt is probably stronger than
the chain anyway, just be sure it is pulled up tight so there is no bending
force on the bolt..

Fine Thread vs Course Thread
 

The foregoing info ignores the following: If the load on the bolt is in
shear (as it should be) and the load is on the un-threaded part of the bolt
(as it should be) then there is no difference in the strength of the two
thread types. Also grade 8s can be bent a long way before they fail and a
good design will limit the amount of bending that can take place anyway. I
would not weld the chain. Welding will anneal the link that you weld on and
substantially decrease it's strength. Using S hooks is a disaster also.
Thru' bolt the chain onto the trailer and shackle onto the vehicle!

wrote in message
...
On Thu, 17 Jun 2004 16:31:27 -0400, "Gary Warner"
wrote:



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) ?


Bear in mind that a machine screw thread is basically an inclined plane
that is
wrapped around a cylinder. Coarse threads represent a steeper incline. You
get
to the top faster, but it takes more grunt power.

If maximum holding power isn't a grave concern, and it's a bolt that will
be put
on and taken off frequently, the coarse threads are "faster", as in less
turns
to remove or install.

BB

Fine Thread vs Course Thread
 

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

Fine Thread vs Course Thread
 

"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.

Fine Thread vs Course Thread
 

"QLW" wrote
The foregoing info ignores the following:

Be that as it may, Bill gets extra credit for posting the first message in
this thread that spelt "coarse" correctly.

Fine Thread vs Course Thread
 

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.



Gene Kearns wrote:
Silly statement. Please provide proof....

Well, that's what the ASCME handbook on threaded fasteners says.

http://www.boltscience.com/pages/glossary.htm

or a better exact quote from
http://www.fastenal.com/web/document...renceGuide.pdf
near the top of page 11
"Fine Thread... offers more resistance to loosening when subject to
vibration than does coarse thread."

Good call on not welding them. Bad call saying that my statements are
"silly" when it's just common sense and a little bit of familiarity with
this range of technical knowledge.

Regards
Doug King

Fine Thread vs Course Thread
 

"Gary Warner" wrote in message ...
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??

If in tension or compression, the fine thread bolt will be superior to
the coarse thread, because there is more surface area. If it is in
shear, then, without thinking too much about it, I'd guess that the
fine thread would win again, because I think fine threads aren't cut
as deep as coarse.