Fine Threads versus Coarse Threads 1

[alan54]

In application where an agitator is secured with bolts in tapped hole, should fine threads be used (rather than coarse threads)? i.e., aren't they less likely to loosen due to smaller incline angle?

 

[evelrod]

Alan---

Assuming the material you are tapping is strong enough to handle the fine threads (not aluminum or castings,etc.) then your on the right track. Fine threads will also give you better control over bolt stretch and clamping force while being torqued down. Keep in mind that a bolt that loosens under vibration is probably caused by improper fit or improper sizeing for the application. A bolt that shears without loosening is probably the wrong size or wrong grade (material).
There are many chemical means to prevent loosening if the size and fit are OK. Mechanical means also (safety wire, split washers, star washers,etc.)

Obviously, this is not a complete answer, just what popped out.


Rod

 

[diamondjim]

Alan,
I think if you are using bolts greater than 3/8 inch
diameter, the fine are ok and allow greater preload.
I would be somewhat concerned about small diameter
fine threads in that stripping could be a problem.
Also if the bolts are short in length your rule
probably is applicable. I am assuming that you
are talking about tapped threads in the parts rather
than thru bolts.