Grade 5 fine thread bolts on a Cub

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Grade 5 fine thread bolts on a Cub

Postby Bob McCarty » Tue May 05, 2015 4:42 pm

I have an opportunity to pick up an assortment of grade 5 fine thread bolts at our local fastener store. He said everyone wants grade 8 and he rarely sells them. I can only think of a few places on a Cub that use fine thread, but thought the collective intelligence of the group will probably come up with a bunch. He wants to get rid of them cheap, and I think he would let me take only the sizes that I want. What is the downside to using a fine thread in place of a coarse thread?

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Re: Grade 5 fine thread bolts on a Cub

Postby ricky racer » Tue May 05, 2015 5:18 pm

There is no downside to using fine thread bolts, however there are very few tapped holes in a Cub that will accept fine thread bolts. The flywheel mounting bolts are one of the few locations I can think of.
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Re: Grade 5 fine thread bolts on a Cub

Postby bob in CT » Tue May 05, 2015 6:30 pm

And muffler clamps on underslung exhaust. I don't think flywheel bolts are grade 5. Add the square head rim bolts and pickings are slim.

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Re: Grade 5 fine thread bolts on a Cub

Postby Larry in WNY » Tue May 05, 2015 7:32 pm

Pan seat bolts are fine thread. Front wheel bolts also. You could always use them for other projects.
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Re: Grade 5 fine thread bolts on a Cub

Postby Bill E Bob » Tue May 05, 2015 11:37 pm

Clamp bolts for the adjustable front axle are fine thread.

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Re: Grade 5 fine thread bolts on a Cub

Postby bythepond88 » Wed May 06, 2015 12:16 pm

I may be wrong (and please correct me if I am), but I believe that, all other things being equal, fine threads have more holding power than coarse threads, so if you converted, it would be only upside, not downside.

The downside, such as it is, would be that you can only substitute them where it is a nut and bolt combo, and you would have to purchase nuts as well as bolts.
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Re: Grade 5 fine thread bolts on a Cub

Postby Eugene » Wed May 06, 2015 12:23 pm

I wouldn't do it. Just buy the fine threaded bolts and nuts as needed.
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Re: Grade 5 fine thread bolts on a Cub

Postby brewzalot » Wed May 06, 2015 6:26 pm

bythepond88 wrote:but I believe that, all other things being equal, fine threads have more holding power than coarse threads


In general, fine threads do have more holding power in steel , but actually less in soft materials such as aluminum. You can get more torque with them and they tend to "hold better" and not come loose as easy as course threads. A ball hitch is a good example of this. A gear puller with course threads is considered weak, and poor quality for this same reason. Another tid bit- threaded bolt holes should be a minimum depth the diameter of the bolt. A 1/2" bolt should go in a hole with good threads at least 1/2" deep. 1.5 times the diameter if going into cast steel.

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