fine thread bolts

Working on my Farmalls over the years they have a lot of places that have fine thread bolts. They aren't as popular these days when you look for them at hardware stores. Were they the more popular bolt to use in their day or was there a reason to use them over course thread bolts.

(quoted from post at 07:03:48 04/21/12) Working on my Farmalls over the years they have a lot of places that have fine thread bolts. They aren't as popular these days when you look for them at hardware stores. Were they the more popular bolt to use in their day or was there a reason to use them over course thread bolts.

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A fine thread bolt has more holding power than a course thread, and a fine thread bolt should always be replaced with another fine thread bolt, and no, you won't find those fine threaded bolts at a general hardware store. Never could. Your local Case-IH dealer is the best place to get those specialty bolts.

Ace Hardware around here has fine thread.

(quoted from post at 07:23:40 04/21/12) Ace Hardware around here has fine thread.

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Yep, they are in the plastic boxes above the regular bolts. Super expensive.

Check with your local Fastenal store. Hal

go down to a local bolt supply house that deals with bolts only

You might find fine thread in a farm store as opposed to a hardware store, these stores usually sell by the pound as opposed to each in a hardware store, at maybe 1/4 the price. If no luck Fasteneal can get them. I do not agree that they are more expensive and rare. They are still common bolts if you go to the right place.

Fine thread bolts have a higher torque rating and more tightening force a can be applied.

Because I can never seem to find a fine thread bolt when I need one I use grade 8 as a replacement.

>...you won"t find those fine threaded bolts at a
> general hardware store.

Actually the local Ace has a limited selection. Of course, it is also a Countryside Coop farm store...

If you buy from Fastenal, thier on-line price is cheaper than at thier store. Also I was able to negotiate price at store when I told them of this fact.

Fine thread bolts have more holding power in sertain materials, but not all. If screwed into soft material (aluminum, plastic, or pot metal for instance, they have much less strength than course threads. If one looks at the minor diameter of fine threads it will be proportionately larger than course threads. this gives fine threads, of equal grade, a small advantage against breakage at the threads over course threads.
Clamping force on a bolt is increased with fine threads up to the tensile strength of a bolt.
Remember, a finger tight bolt will hold a bumper on a truck with all its tensile strength.
a bolt tightened to 90% of its tensile strength will only hold 10% of its strength!!!!
Thus the reason for torque requirements on lug bolts to keep them within the strength required to hold the wheel on.
Compressing a head gasket is similar in that once it seals, more tightening just reduces the strength of the force holding the head against combustion pressure.
Yield strength and bolt stretch, turn of bolt systems, and torque are for another day. Jim

I know the thread Nazis will get me but I have been know to re thread a fine thread dot bolt with course threads when the bolt was rare and special. Yes the fine threads were stripped out. There are some bolts that are just very hard to replace. Of course it will only work when the nut can also be replaced.

(quoted from post at 07:47:19 04/21/12) You might find fine thread in a farm store as opposed to a hardware store, these stores usually sell by the pound as opposed to each in a hardware store, at maybe 1/4 the price. If no luck Fasteneal can get them. I do not agree that they are more expensive and rare. They are still common bolts if you go to the right place.

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I am saying they are expensive when you buy them from the bins on top of the regular bolts.

Fastenal's around here are kind of jerks about selling small quantities to private people. They are "corporate only" is the line you get. When they do sell to you they charge you full mark up.

Farm and Fleet/Fleet Farm/TSC don't have bulk find threads around here. Only Grade 2, Grade 5, and Grade 8 course bolts and nuts. Same plastic bins or little bags of bolts or nuts.

Menards has really good hardware prices if you have a Menards near you. I can't speak for fine thread, but I needed galvanized carriage bolts and they were cheaper than all the stores mentioned above (if they even had them).

> a bolt tightened to 90% of its tensile strength
> will only hold 10% of its strength!!!!

Not true. It will hold 90% of its tensile strength (though it's usual to tighten to 75%). The bolt experiences no additional load beyond its preload until the force pulling the clamped components apart exceeds the preload: until then there is no gap between the parts and there for no extension of the bolt (and of course as soon as a gap appears the joint has already failed).
Bolted Joint

your argument seems valid, but if that were the case, tightening bolts to within a few % of failure would be strongest. Forces are additive. Jim

Over here the bolt situation is a bit of good and bad. I have found a place that sells UNC, UNF, BSW and BSF bolts at very reasonable prices. Their motto is "anything with a thread". I got 8 new 7/8 UNC bolts and spring washers for the steel rear wheels on my H for $30. The problem with Farmall tractors in Australia is that many of the Australian assembled and manufactured parts use BSW bolts in place of UNC. ½" BSW has 12 threads per inch and ½" UNC has 13. Very easy to damage components quickly. I always replace coarse thread bolts with coarse thread and fine thread bolts with fine. Often the IH catalog gives the tensile strength required. For example front hub cap bolts are listed as Grade 5 - somewhat over engineered I think!
SadFarmall

> your argument seems valid...

It's the argument engineers have been making for a couple of hundred years. I first heard it from Dr. Peach in the 1960s. It's correct.

> ...but if that were the case, tightening bolts
> to within a few % of failure would be strongest.

That would work if you knew exactly how strong each bolt was and if you could be certain that the tension in the bolt was exactly proportional to the torque. Because of friction it isn't, and the friction varies.

> Forces are additive.

Forces are vectors. The bolt tension clamping the parts together and the load trying to pull them apart point in opposite directions.

Consider a pair of castings held together by a bolt with 10,000lb tension in it. There's 10,000lb of tension in the bolt and 10,000lb of pressure between the castings. Thus the total force is zero (as it must be or something would move).

Now hook the assembly to a couple of tractors and start pulling on it with 5,000lb of force. You now have 5,000lb tension in the chains trying to pull the castings apart, 5,000lb pressure between them trying to push them apart, and 10,000lb tension in the bolt holding them together. Total: zero. The bolt is still carrying only its preload.

Crank the pull up to 10,000lb. You now have 10,000lb tension in the chains trying to pull the castings apart, zero lb pressure between them trying to push them apart, and 10,000lb tension in the bolt holding them together. Total: zero. The bolt is still carrying only its preload.

Up the force to 15,000 (you're using a couple of Steigers) You now have 15,000lb tension in the chains trying to pull the castings apart, zero lb pressure between them trying to push them apart (there will now be a gap: the joint has failed) , and 15,000lb tension in the bolt holding them together. Total: zero. Only now, when the load on the joint has exceeded the preload, does the tension in the bolt exceed the preload.

This analysis assumes that the castings are totally rigid. There is a small error due to the fact that they are actually compressible, but in most applications this error is negligible because the parts are much larger than the bolt. In some special cases (soft materials, odd shapes) this is not true.

Always torque all bolts to spec. Under torquing leads only to loosening and failure.

Please take a look at the Bolt Science tutorial linked below. Lots of good stuff on that site.



And, to open another can of worms, throw away the split ring lockwashers.
Bolt Science tutorial

First of all I agree with your assessment of split lock washers. A study was done by a group of engineers with Gary Nut and Bolt (no longer that firm, sold several times) that placed the split lock washer as a prime culprit in thousands of fastener failures. It neither digs into the base metal not nut well enough to resist loosening, nor does it work sat all with a flat washer under it. and beyond cracking it two and falling out, it provides point loading to surfaces it contacts at its pawl shaped split. Throw them in the weeds!!!
Star washers are little better.
Locktite, Nyloc, Deformed thread nuts, Castile nuts and cotter pins, even jamb nuts are better.

I think we agree on much. I also think the stress on a rigid component with a non stretchable fastener will act as you described.
Many assemblies do not comply with ideal. Metal bends and compresses becoming a spring under the head of a bolt that itself has become a spring.
Which bolt would you trust more to hold your bungy jumping anchor? The first is bolted through a 6"X4" heavy walled tube in the 6" direction and through a forged steel bracket that pulled straight (axially) on it, tightened (stretched)to 75% of yield. or one that was identical and tightened to 5% of yield. Springiness changes the reality. Jim

> Which bolt would you trust more to hold your
> bungy jumping anchor? The first is bolted
> through a 6"X4" heavy walled tube in the 6"
> direction and through a forged steel bracket
> that pulled straight (axially) on it, tightened > (stretched)to 75% of yield. or one that was
> identical and tightened to 5% of yield.

The first one, of course. The second is going to loosen up, fall off, and kill somebody. You can't do much worse than combine an under-torqued bolt with a cycling load.

(Yes, I realize that the tube will compress a bit. The engineer who designed the joint will have taken that into consideration. He will also have allowed a safety margin of at least 10.)

> I also think the stress on a rigid component
> with a non stretchable fastener will act as you
> described.

I missed this before. The analysis necessarily assumes that the bolt is stretchable. The whole point of torquing bolts is to stretch them. The stretched bolt acts as a spring clamping the parts together.

ergo shared load. Jim

I was here 2 months after it failed.
Also related DC10 from Chicago left engine twisted off wing. Jim
interesting and only partially related

Jim, The engine on the United DC-10 had a fuse pin failure as I recall. The bolt just was to hold the fuse pin in place and wasn't a real load bearing component. The fuse pin is a cylinderial machined piece which held the engine strut or plyon through it's mount to the fittings on the lower wing structure and the bolt was only something probably less then a .500 inch diameter merely to keep the fuse pin in place. Those engine attachments were usually line bored on installation with the straightness and hole size tolerence of something like +.0005/-.0000 while the fuse pin was probably super cooled in liquid nitrogen at installation - assuring a very precise fit. There are also very close limits on the amount of pre-load at installation that can be applied through wing deflection to permit strut to wing installation. I didn't work on the McDonnell Douglas products but know their installations were very similiar to those we used at Boeing back in my pre-retirement life, Hal.

You compensate for shared load by increasing the bolt size, not decreasing the preload. The tutorial at the Bolt Science site covers the exact analysis in gory detail. Lots of other good stuff there too, such as a discussion of bolting and gaskets.
Bolt Science tutorial

Here's an example that's more to the point:
Under torqued Bolt

John, I'm glad to see you got into this discussion which I had thought about doing, but decided I did not want the hassle. I have told many folks that bolts must be tightened to torque specs in order to avoid fatigue failure of the bolts. As you correctly stated, the bolt does not experience any additional force until the force on the system exceeds the clamping force of the bolt. Hard for lots of folks to understand this. Thanks for having this discussion!!

(quoted from post at 20:00:56 04/21/12) your argument seems valid, but if that were the case, tightening bolts to within a few % of failure would be strongest. Forces are additive. Jim

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The strenght of the bolts does not change. The objective is to have a clamping force greater than the force acting on the joint. This minimizes cyclic loads on the bolts which leads to loosening and or fatigue failure.