Rim bolts - why fine thread?

[CapeCodCubs]

I have my new rims and turfs ready to mount to the centers and had to get new square bolts. Square head 1/2 - 20 and everyone knows they are pricy.
I ordered from TM for $4.95 each but decided to cross reference the Deer part number and found after I ordered ARKS Tractor has (had) them for $1.86 each. So I ordered their last 8, just to have a set for the next rims and tires I do...soon. Such a scarce part.

After looking at what I had after dismounting some early 7-24's from the centers is they used 1/2 -13 threaded square heads. The tires and rims were original tires, so maybe someone replaced the rim bolts. What is the reason for the fine thread? Why couldn't anyone use a grade 2 square head 1/2-13??

[Rick Spivey]

My semi-educated guess is that the engineers felt that standard threads might vibrate loose over time and use. Fine threads are much harder to shake loose due to use. Beyond that, it's beyond me.

[tldec50]

What Rick said,fine threads are stronger and they have more gripping area as to course threads

[CapeCodCubs]

What Rick said,fine threads are stronger and they have more gripping area as to course threads

That and more turns to back off, but the ones on the rims I took apart had lock washers and were set in place good. Lug nuts are fine thread so it must have been an industry standard.

[Cubfriend]

Fine threaded bolts also have more clamping power with the shallow angle of the threads. IH used a lot of fine threaded bolts in many applications.

[Clemsonfor]

Fine threaded bolts also have more clamping power with the shallow angle of the threads. IH used a lot of fine threaded bolts in many applications.

I was going to say this. Well about the clamping power not necessarily about IH useing lots of fine thread.

[SamsFarm]

The thread angle is the same (60°) whether you have a coarse or fine thread (American inch fasteners).

The difference is the fine thread has a larger root diameter.

Also the fine thread provides more clamping power and is easier to torque!

You have to turn that fine thread fastener more turns to go the same distance!

Example:
A 1/2-13 takes 13 complete turns to travel a inch.
Each thread is equal to .0769"

A 1/2-20 takes 20 compete turns to travel a inch.
Each thread is equal to .050"

Hope this helps!

[SamsFarm]

Another thing to consider for your wheel screw and bolt grade is the shear forces at work against them.

The rear lug screws on my 68 cub are grade 5, IH head stamp, so I would recomend grade 5 or better for replacements!


Your Cub c60 engine probably makes 30 to 40 foot pounds of torque (guessing).

Take that engine torque and times that by the 1st gear ratio (?), then times the ring and pinion ratio (?), then times the ratio of the final drives (?).

I do not know what the cub has for gear ratios, but your engine torque, by the time it gets to the rear axle will be significantly higher!

If anyone knows the different gear ratios, please tell us!

[Jim Becker]

. . . If anyone knows the different gear ratios, please tell us!

I believe all the tooth counts are in the parts catalog.

[Super A]

IH used a lot of fine threaded bolts in many applications.

They sure did--in a lot of places there was absolutely no need for fine threads! They're good for rim bolts and such but IH had fine threads holding a lot of sheet metal, brackets, etc. together. They are much more aggravating to take apart when they've been on there for 70+ years!

Al