Could somebody please tell me why the different thread pitches? Is fine thread stronger or weaker than normal/coarse thread? Where on the car, and why, would you use one instead of the other?

Thanks in advance for any help/advice,

Cheers chaps,

Martin.

It's a very complex subject, all too frequently overlooked by the inexperienced. There are so many variables that it's not easy to give straightforward answers to your questions. Two bolts the same diameter and length, one in tension, the other in shear, can be vastly different. Also, the material of the female thread can determine whether coarse or fine threads are appropriate.
Best you have a read of some theory and specifications. The following may get you started:
Bolt Science.
Earnest.
IF.
Maryland Metrics.
ARP.

Hi.

One application of fine threads (IMHO) is when adjustment is needed.

I'm thinking in particular of suspension joints.

I have used rod ends on my rear bones that have a coarse thread.
I wish I'd have used fine threads as this would give me finer adjustment
of wheel alignment and camber.
At least a rod end can be screwed in or out half a turn at a time so they may be OK.

I can but hope.

Paul G

As mentioned finer threads are better when small adjustments are needed.

As for materials, bolts etc fitted in to soft materials (eg aluminium) are less likely to pull out or rip the threads if they are fine as there are more threads engaged. But as Rorty says this gets quite complicated on which thread to chose for a cretain application.

I tend to use fine threads for the above anyway.

David

quote:

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Originally posted by flak monkey
...bolts etc fitted in to soft materials (eg aluminium) are less likely to pull out or rip the threads if they are fine as there are more threads engaged.

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OK...I'll shoot the guy that told me that then....

Aggree wit the above and would add the following.
If you think of the thread as working like a wedge, the course thread is a thick wedge and the finer ones would be a very thin wedge.
Drive a thin wedge into a gap and the force is huge, therfore, the fine threads apply much more force and generally can be torqued to higher amounts.
the materials of the female thread is very important though as stated above.

Also, the core of the fine-thread bolt is thicker than that of the coarse-thread one, so is stronger.

To say a bit in favour of the coarse thread, the thread itself is stronger, and also it is much more suitable where the thread is likely to get muddy or dirty - it's less likely to jam up solid.

But, as said above, it's a complex subject.

David

Think also on the bolt loosing part....

To undo a fine thread nut you need to turn it much more revs then the other one...

as about of strengt you need the middle way, because a strong thread with a week inner body isn't usefull soow same for strong body with weak thread..

then you have to compare the 2 bolts wo weight the same (more material more strenght)

also you need to think that a bolt with much more thread (finer) has a bigger contact surface with the other one

soow loosening is also overthere braked (more resistance)

TKS

Coarse threads apart from use in light alloys and cast iron coarse threads are excellent for bolts exposed to road muck and salt such as on exhausts.

Cheers guys, thanks for all the input. Much appreciated.

Martin.

If you want to get seriously into bolts and bolted joints then this is THE bolt bible.