Fine thread bolts vs coarse

[Josh]

I use my judgement, I try to use the original bolt type but sometimes you can't find or wait for an order of grade 8 fine threaded bolts. What ticks me off about rusty fine threaded bolts is the threads can break and the bolt just spins in place. Good if you want to keep the part together, bad if you want to remove the part!

I recently did a tow hitch install and noticed the Curt 18,000lb trailer hitch and Reese 16,000lb ball and pintle both came with grade 8 coarse threaded bolts for the install. The ball however was fine threads. If grade 8 course threaded bolts are good enough for towing...well....? I do make sure to use lock washers or thread locker after a bad experience loosing a leaf spring bolt on a trailer once.

My curt hitch also game with grade coarse threads. 3 of them sheared off with in a week towing a trailer way under max weight for the hitch. Switched em to fine thread and have yet to have a problem.

 

[John S-B]

As a general rule when a bolt goe into some thing it is coarse tread
And when 2 pieces are bolted together it is fine
Now if you want to change all off your bolts you better not sell the truck because the next guy will have a problem off knowing whether it is coarse or fine.
Willy

SELL THE TRUCK???

 

[John S-B]

I also chase the threads on every bolt I remove and chse the threads witha die if needed. Every bolt I remove gets anti sieze in it, no matter what. You never know when you will have to take it apart again. Especially when it is easier to remove three thigs to get at the one thing you have to work on, Look around, you can always find a supplier of finethread bolts either locally or on line. Stop shopping at Home Depot, When you shop at Home depot, you get cheap. When you get cheap, you wind up painting your deuce with house paint.. Don't paint your deuce with house paint

Rapco 24087 Baby!!

 

[John S-B]

Hey thanks for all the good info guys, I think I'm going to make a trip down to Fastenal this afternoon. I'm going to try and save some of the bigger bolts (1/2" and up), but the smaller stuff I think I'll replace. It's just not worth cleaning all the rust and chasing threads on those.

 

[clinto]

My curt hitch also game with grade coarse threads. 3 of them sheared off with in a week towing a trailer way under max weight for the hitch. Switched em to fine thread and have yet to have a problem.

Holy crap!!!!! Really??!!!!

I guess I should consider replacing the hardware that came with mine.

 

[Atomic]

Fine is generaly used for high vibration use. More contact in the threaded areas. Switching to a coarse thread bolt will not down grade your clamping force, although, a fine thread does have a slightly higher clamp load.

SAE J429 Standards 1/2" example:

1/2-13 9046lbs
1/2-20 10197lbs

Generally, if it says grade 5, I put a gr5 back on. Fine vs Crs, mehahhh but the price between the two is considerable.

 

[Katahdin]

Re Curt hitch, is it possible the nut spun off the carriage bolt? I noticed mine didn't come with lock washers.

 

[EMD567]

I always try to use fine thread, and I ALWAYS use locking nuts of some kind.

 

[cattlerepairman]

Stop shopping at Home Depot, When you shop at Home depot, you get cheap. When you get cheap, you wind up painting your deuce with house paint.. Don't paint your deuce with house paint

 

[F18hornetM]

I agree using what came out is smart, and keeps original but alot of fasteners on these trucks are not "critical" fasteners. I can see where on some components such as chassis parts etc, would be good to keep Fine thread. But Alot are just body/accy bolts and such and no real need for fine thread other than keeps original. To each their own of course.

 

[lavarok]

I agree using what came out is smart, and keeps original but alot of fasteners on these trucks are not "critical" fasteners. I can see where on some components such as chassis parts etc, would be good to keep Fine thread. But Alot are just body/accy bolts and such and no real need for fine thread other than keeps original. To each their own of course.

Good example is the bolts that hold the mud flaps in place.
I had to swap a mudflap, lost a fine thread fastener and swapped in a course thread bolt and nut from my "misc" box. I think for this application it will be fine.

Most of the time I'd head over to the local ACE hardware to source direct replacements to match the originals. I try to replace any bolts with new when I disassemble and reassemble large components, such as fenders.

 

[DHennon]

FIne thread vs. Coarse thread

I too, have spent almost as much on grade 8 fine thread as I did for the whole truck! I have a Friendly Hardware Place close by with sizes up to 2" Fine and coarse.

 

[Josh]

Re Curt hitch, is it possible the nut spun off the carriage bolt? I noticed mine didn't come with lock washers.

Its possible, but I put lock washers on as mine didnt either. I torqued them to spec and everything. Maybe I had a bad run, idk, but having the receiver fall off the truck is not a good thing. Well worth the extra 10 bucks the fine thread and nylocs cost.

 

[04mustang]

I find this thread very intresting...no pun intended,
I am a degreed engineer and have had a couple of classes that relate to this very subject. What is intresting is that from an engineering stand point there is no difference in the corse vs. fine thread argument. The only reason that the military would prefer the fine thread is because of the vibrations in these type of applications. However, structually there is no difference, so long as the diameter of the two bolts does not change (size).



Another intresting fact: if youve ever wondered if you can shear the threads off of a bolt/nut when tightening it, you can now sleep peacefully at night. That is impossible from an engineering standpoint. BUT.....you very easily can shear the bolt in half.
The reason for this is that it will always require less force to shear a bolt in half than what would be required to strip the threads off.
....just food for thought

Thanks,
Corey

 

[Cleveland Iron]

I've picked up so many fine threaded bolts that the local hardware store they asked me to park the truck in the lot for advertising. (Yes, we even had parts for this.)

 

[John S-B]

Went down to Fastenal and ordered 6 doz. 3/8" bolts in 3/4, 1, and 1 1/4" lengths with nuts and 2 dozen washers. I also got 2 doz. 1/4" pan head bolts and nuts. It was about $65 for all of that. Grade 5 also.

 

[misupratwin]

Another intresting fact: if youve ever wondered if you can shear the threads off of a bolt/nut when tightening it, you can now sleep peacefully at night. That is impossible from an engineering standpoint. BUT.....you very easily can shear the bolt in half.
The reason for this is that it will always require less force to shear a bolt in half than what would be required to strip the threads off.
....just food for thought

Thanks,
Corey

I have worked in dealerships and owned my own auto repair shop for 20 years and i have taken the threads off alot of nuts and bolts tighten them with my snap on impact. Although they weren't always in the best shape.But a few were brand new grade 8 bolts while installing my winch.

I always use grade 8 or grade 9 fine thread bolts and grade 8 top lock nuts for all my military repairs or additions .

 

[F18hornetM]

Where I work we work on aerial devices. Bucket trucks, 36'-96' models and diggers etc. On a 36' aerial device [man lift] there are only 8 bolts that hold the tower to the sub frame. They are course thread as is all the bolts we use. I can't recall any bolts in the aerial units being fine thread. If its good enough to hold a man up in the air I'm not to concerned with course vs fine thread.
I dont want to say its a waste of money to put mud flaps or a fender back on with fine thread bolts as its each persons project and everybody has their reasons. For me, its a waste of money. I seriously doubt it will degrade the re-sale value as well. Again just discussion as I see others point of view.

 

[m16ty]

When I take a bolt out, if it's still good I but the original bolt back. If it's bad I usually go back with a course thread. More times than not when you remove a fine thread bolt on one of these old trucks, it will be bad.

 

[Katahdin]

I've read the argument that the bolts is a good reason to buy a parts truck, but I sure wouldn't want to have bought my truck for the bolts! I've had to cut off too many to count because the rusty threads stripped. The threads on the bumper bolts I've removed were all mangled too.

I have my wife convinced that whenever I say "I'm going to Tractor Supply to buy some bolts" that I'm actually leaving to go visit a girlfriend!