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Tool Talk Discussion Forum

fine vs course thread bolts

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charlie M

09-22-2013 12:48:35




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Any advantage to a fine thread bolt over a course thread. Fine threads seem to be more difficult to find.




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dr sportster

09-22-2013 17:20:24




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
Generally fine threads are for clamping force on parts to a fine thread nut and coarse threads have less chance of pulling out of a casting. An example would be a stud on a Harley base nut. coarse screws into the aluminum crankcase and fine sticks up for the nut to hold the iron cylinder down tightly. But as I said generally.You can google lots of info on this.



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55deere70

09-22-2013 15:39:00




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
That's why for applications requiring high tensile strength like head and main bearing bolts, fine thread fasteners are used almost exclusively.
Really? Most head bolts and main bearing bolts I've seen are coarse thread. I don't think fine thread would last long in cast iron or aluminum.



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GVSII

09-30-2013 14:38:50




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 Re: fine vs course thread bolts in reply to 55deere70, 09-22-2013 15:39:00  
Quoting Removed, click Modern View to see
Head STUDS into the block-coarse thread. Head studs THROUGH- the head-fine thread.



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GVSII

09-30-2013 14:37:50




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 Re: fine vs course thread bolts in reply to 55deere70, 09-22-2013 15:39:00  
Quoting Removed, click Modern View to see
Head STUDS into the block-coarse thread. Head studs THROUGH the head-fine thread.



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Bob

09-22-2013 16:57:02




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 Re: fine vs course thread bolts in reply to 55deere70, 09-22-2013 15:39:00  
As an example, Cummins V8-470 and V-8 504 engines have fine- thread head bolts going into cast iron. Probably some pretty good stuff, maybe high nickel content???

Been so long since I worked on a 855 or other big Cummins I don"t remember if those bolts are course or fine.



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36 coupe

09-22-2013 15:00:26




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
COARSE.Course is a golf course.Threads weaken a bolt.



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charlie M

09-22-2013 16:26:34




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 Re: fine vs course thread bolts in reply to 36 coupe, 09-22-2013 15:00:26  
I have to plead insanity on this one.



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Dusty MI

09-22-2013 16:59:04




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 16:26:34  
I made a puller once, to pull a brake drum off the axel on a tractor. I used a fine threaded bolt thinking that it would have more pulling power. I stripper the threads off the bolts. Would a coarse threaded bolt have worked better? I don't know, I gave up and used another approach.

Dusty



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dr sportster

09-22-2013 17:22:57




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 Re: fine vs course thread bolts in reply to Dusty MI, 09-22-2013 16:59:04  
For making pullers it is best to order a rod of square or acme thread for the most force .One three foot piece can make alot . Or old jacks are a source too. MSC sells rod.



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MarkB_MI

09-22-2013 14:52:45




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
For a given grade, a fine thread bolt has higher tensile strength than a coarse thread bolt. That's because the threads on a fine thread bold aren't as deep, leaving more of the bolt diameter.

Check out the table at the site below. A grade 5 1/2-13 bolt as a tensile strength of 17,000 lbs. For a grade 5 1/2-20 bolt, it's 19,200. That's why for applications requiring high tensile strength like head and main bearing bolts, fine thread fasteners are used almost exclusively.

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Dean

09-22-2013 15:11:35




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 Re: fine vs course thread bolts in reply to MarkB_MI, 09-22-2013 14:52:45  
Bingo.

Fine thread fasteners have less thread engagement. This is the reason that fine thread fasteners are not recommended for use in materials such as cast iron, aluminum, etc.

Dean



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60 acre hillside

09-22-2013 14:47:01




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
Henry Ford loved them. I have found that proper choice of fasteners are usually used in the right places. I could never understand why Ford used fine thread on plow bolts.



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Dr. Walt

09-24-2013 14:22:59




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 Re: fine vs course thread bolts in reply to 60 acre hillside, 09-22-2013 14:47:01  
60 acre hillside:

"I could never understand why Ford used fine thread on plow bolts."

To get you to BUY MORE plow bolts when the threads stripped out!



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greygoat

09-22-2013 13:37:57




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
I find fine threaded,(SAE) bolts/nuts at Menards,
(China), Home Depot, "Blains Farm-Fleet", and,
of course "Fastenal"



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dpendzic

09-22-2013 12:52:34




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
that are less likely to work loose---a good lock washer on a course thread helps a lot



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DouginIL

09-22-2013 12:52:24




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
Fine threads can be torqued to higher values for a given diameter and grade of bolt.



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dpendzic

09-22-2013 14:16:09




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 Re: fine vs course thread bolts in reply to DouginIL, 09-22-2013 12:52:24  
actually the limiting factor is the yield strength of the bolt. If you need more torque to produce the the same clamping force desired then a fine thread would not be as efficient as a course thread



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Brian G. NY

09-22-2013 14:52:21




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 Re: fine vs course thread bolts in reply to dpendzic, 09-22-2013 14:16:09  
You gotta run that by me once more dependzic!
I'm no engineer, but I think what Dean says sounds reasonable.
After all, walking up a less steep ramp gets you there the same as a steeper ramp but it's just a little easier walkin'.



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dpendzic

09-22-2013 16:24:34




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 Re: fine vs course thread bolts in reply to Brian G. NY, 09-22-2013 14:52:21  
what i am trying to say is that fine thread has more threads per inch so the friction working against the torque applied is greater. However the strength of the bolt is determined by the yield strength of the steel--not the tensile strength--the limiting area is not the root diameter of the threads but a greater value A- sub t--determined by tests--and of course fine threads have a greater area than course threads so the ultimate allowed clamping force will be greater-but a slightly more torque will be required to obtain that.--In real life situations it is probably insignificant unless you have a required clamping force required. In all of NY state bridge design connection requirements it is standard to use course thread A325 7/8 diameter bolts tensioned to a load of 30000 lbs.-
The torque wrenches are calibrated each day with a load cell---sometimes load indicating flat washers are used---lock washers are never used.

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Joe(TX)

09-22-2013 17:04:41




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 Re: fine vs course thread bolts in reply to dpendzic, 09-22-2013 16:24:34  
It's time for and engineering lesson.
Tensile strength and yield strength are material properties. The tensile load capacity of the the bolt is determined by the tensile strength an the cross sectional area of the bolt.
A fine thread bolt has a larger cross sectional area. There for it will carry a largr tension load.
All bolts in a bridge are loaded in a shear configuration. That means it is loaded across the diameter and not lengthwise. The thread type has no effect in this type of loading. It is also important that the thread area is not at a shear location as this will decrease the area.
The torque load fo the bolt is designed such that the working stress never exceeded the torque stress. This insures that the bolt will not fatigue.

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dpendzic

09-22-2013 18:08:56




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 Re: fine vs course thread bolts in reply to Joe(TX), 09-22-2013 17:04:41  
have to disagree Joe on the connections being in shear on the bolts. The connections are designed as friction connections with no shear load on the bolts--thats the reason for the very high clamping load to produce this friction.



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Joe(TX)

09-23-2013 18:42:38




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 Re: fine vs course thread bolts in reply to dpendzic, 09-22-2013 18:08:56  
You are mistaken. A bolt joint does not rely on clamping friction. I have been an engineer for over 40 years, and only an idiot would rely on friction for a connection.
If you have two plates bolted together, they have a shear connection.



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Owen Aaland

09-24-2013 09:00:00




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 Re: fine vs course thread bolts in reply to Joe(TX), 09-23-2013 18:42:38  
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If you don't think friction plays a part just install a flywheel with the bolts only snugged up a bit and see how long the bolts last by themselves



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dpendzic

09-24-2013 06:16:03




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 Re: fine vs course thread bolts in reply to Joe(TX), 09-23-2013 18:42:38  
well never thought I was an idiot as being a licensed structural engineer in two states , having designed close to two dozen bridges, and retired as the Director of Bridges and Structures for a county in NY. I certainly hope those bridges don't fall down!



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Dean

09-22-2013 12:51:40




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 Re: fine vs course thread bolts in reply to charlie M, 09-22-2013 12:48:35  
All else equal, fine threaded fasteners produce more clamping force than course threaded fasteners at the same tightening torque and are less prome to self loosening.

Dean



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