OT Threads: fine vs course

[Machine249]

What is the difference between fine threads and course threads? Apart from the obvious thread count. For instance, when would one be an advantage over the other. It seems to me that course threads would be stronger and therefor more desirable. Thanks for any input or opinions.
 

[Hec In Omaha]

Fine Threads have a higher Tensile Strength.
 

[Dean]

Fine threaded fasteners provide a higher clamping force for a given torque than course threaded fasteners.

Course threaded fasteners have a deeper thread engagement and are preferred for use in soft or brittle materials such as cast iron. They are also less expensive to manufacture.

Dean
 

[TheOldHokie]

[Machine249]

Thanks for the repies fellas. There is some very good information here. Something for me to keep in mind when fabricating and/or restoring parts. Thanks again.
 

[Del Huebner]

Very good information, just printed a copy off for my notebook.
 

[John,PA]

Fine threads are most common in aviation fastners. Howevers, what makes me nervous are 'dem ultra-lights and home builders.

John,PA A&E. EXPERIMENTAL equipment is all that is necessary for placards.
 

[Maineman]

Boy, thought I could contribute something here!
But, oldhokie pretty much covered it!
I will add that there are also different classes of threads. And English thread standards are different than American. And European metric threads are different than American metric threads.

Not trying to show off, just trying to use some of that knowledge I gained over the years!

Joe
 

[Machine249]

That's interesting Maineman. One of the things I really like about working on these old tractors is that everything is pretty well standard. These old tractors and my Harley are the only things I don't have to go back and forth to the tool box a hundred times to get the right wrench. I restored a Farmall a few years ago and you can take those 75% apart with just a 9/16" wrench.
 

[BMACK518N]

There are a few schools of thought on when to use a coarse vs fine thread. Most machines are engineered the way they are around those thoughts. Being in the bolt & nut business for over 37 years I've seen people make some bad choices in fastener selection even with best advise.
TOH has listed some good points regarding thread selection for your project.
Metric fasteners are another ball game. German vs Japanese fasteners can give you up to 4 different theads for one diameter, different wrench sizes for industrial vs automotive and it's a true learning lesson figuring out the bolt hardness. I would hate to be a true mechanic these days with the added expense of tooling up to do your job. As a fastener distributor I'm use to metric conversions, as an "American" I refuse to convert anything to metric.
At the end of the day would be believe fine thread fasteners are a nickle and a dime more than coarse thread. Just my two cents.
 

[TheOldHokie]

[BMACK518N]

TOH,
You are so right, our own system was in bad shape for so long before some standards were set in place. Most people will never understand the machinists side like you do. My Dad was a jet mechanic all his life and had so many specialty taps and dies that when he passed away I gave them to a friend of his that was a machinist as I had no use for them. Irony of it all I was an ADJ in my short career in the Navy. I did keep one tool as a memory and that was a pair of safety wire pliers that I still have. Some people think I was born with this flat spot on my head. My Dad put it there after misusing many of his tools such as the safety wire pliers for cutting bicycle spokes. If nothing more than respect for tools I appreciate the common sense he passed on.