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coarse vs fine thread bolts

C

Charlie M

Well-known Member
Is there a reason for using fine thread bolts vs coarse thread bolts on the old tractors. Seems like at least on my Farmalls the metal work tends to be fine thread bolts when all the bigger bolts are coarse thread. I took the operator plate form off my BN last night and it was mostly fine thread.I think most of the grills on my tractors use fine thread.
 
(quoted from post at 12:26:56 08/12/20) Is there a reason for using fine thread bolts vs coarse thread bolts on the old tractors. Seems like at least on my Farmalls the metal work tends to be fine thread bolts when all the bigger bolts are coarse thread. I took the operator plate form off my BN last night and it was mostly fine thread.I think most of the grills on my tractors use fine thread.
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I don't know the reason unless you tend to get less problem with loose fasteners on tractors by using fine threads. My 53 NAA and 70 model 4000 all have fine thread fasteners on all the bolts 7/16 and under, coarse thread for 1/2 and larger as a rule. Even the 5/16 battery hold downs are fine thread. There must be a good reason or it would not be wide spread among the various manufacturers.
 
Course threads are stronger in iron castings, and alloy components because the shear strength of the overlap between major diameter and minor diameters (engagement of threads)is weaker in those castings and alloys. Bigger thread forms are less likely to strip. In steel fasteners, and fittings fine threads work well, and can clamp better. Jim
 
Generally a coarse thread is used in a casting or fully threaded hole where a fine is used to pinch parts together strongly.
 
Fine threads also leave more metal in a stud or capscrew as the threads are less deep than course threads.
 
i think it has to do with vibration. a fine thread will not vibrate loose as quick . even the valve cover studs are fine thread. fine thread also takes a higher torque.
 
(quoted from post at 10:17:20 08/12/20) i think it has to do with vibration. a fine thread will not vibrate loose as quick . even the valve cover studs are fine thread. fine thread also takes a higher torque.
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That is what I have heard also.
 
Fine thread , yes is a good snug down bolt, takes more torque, the next step up would be a hard bolt, #5 or #8.
I agree, will take more vibration before loosening. My father had an old MAssey Harris Clipper combine, and over time he acquired two more for parts. They were mostly all fine thread bolts. I still have cans of 5/16, 3/8 , 1/2, 7/16 bolts!!
 
All of the WW2 and Korea era military vehicles I have restored have been almost exclusively fine threads for the fasteners. The only coarse threads are in engines and power train components. If a body or frame part has coarse threads it is because a civilian owner has added those bolts. Fine threaded fasteners do strip threads easier because fine threads are shallower .
 
(quoted from post at 08:26:56 08/12/20) Is there a reason for using fine thread bolts vs coarse thread bolts on the old tractors. Seems like at least on my Farmalls the metal work tends to be fine thread bolts when all the bigger bolts are coarse thread. I took the operator plate form off my BN last night and it was mostly fine thread.I think most of the grills on my tractors use fine thread.
Click to expand...

Pretty much just B.S. or an "old mechanics wives' tale".

Don't think DEERE bought into that nonsense, or even "Binder", for the most part, as I recall, just the oddballs like Ford and Massive Ferguson.

Can't recall any fine thread bolts used on the sheet metal of tractors made in the last 50 or 60 years, and the bolts don't seen to fall out of 'em.
 
Fine thread bolts are so the junk man has something to haul away. They always stripped easier for me and didn't hold the job as well. IF a bolt comes loose it is not big enough. I have had plenty of bolts that if you could go to the next size bigger it would then not work loose. Fine thread are for bending into loops or rings to weld on to something where you need a ring or loop. Thats my story and I'm sticking to it.
 
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