A nerdy question about Stover nuts and torque

Stinkbug

Stinkbug

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Stover nuts, metal, locking nuts whatever you want to call them have a certain amount of resistance before they even snuggled up. How do you account for that when you’re trying to get to a certain torque setting for a fastener?

For example, if you are using a standard nut and bolt and you torque it to 50 pounds I think would give you a different clamping force than if you torque a bolt and stover nut to 50 pounds. Is that true or am I overthinking this?

This question popped into my head last night as I was counting ceiling tiles, waiting to fall asleep. The reason I was thinking about this is I’m getting ready to reinstall my freshly rebuilt shocks on my Jeep. The factory torque setting for the lower rear shock bolts is somewhere around 55 pounds. My outboard shocks use Stover nuts and I don’t believe that if I torque them to 55 pounds I’ll have anywhere near the clamping force of a traditional nut and bolt torque to 55 pounds.

I think the real answer is twist them they are tight and there’s no movement, but just curious what those who have experience with fasteners think about this on a grander scale.
 
Stinkbug said:
Stover nuts, metal, locking nuts whatever you want to call them have a certain amount of resistance before they even snuggled up. How do you account for that when you’re trying to get to a certain torque setting for a fastener?

For example, if you are using a standard nut and bolt and you torque it to 50 pounds I think would give you a different clamping force than if you torque a bolt and stover nut to 50 pounds. Is that true or am I overthinking this?

This question popped into my head last night as I was counting ceiling tiles, waiting to fall asleep. The reason I was thinking about this is I’m getting ready to reinstall my freshly rebuilt shocks on my Jeep. The factory torque setting for the lower rear shock bolts is somewhere around 55 pounds. My outboard shocks use Stover nuts and I don’t believe that if I torque them to 55 pounds I’ll have anywhere near the clamping force of a traditional nut and bolt torque to 55 pounds.

I think the real answer is twist them they are tight and there’s no movement, but just curious what those who have experience with fasteners think about this on a grander scale.
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Simple method would be to see how much torque it takes to turn the Stover nuts before they bottom out and add that to your torque value. I am however, practically certain that an engineer will be along shortly to correct that since I've never seen it talked about anywhere.
 
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Head Lice said:
Same type of scenario is lubed vs dry fasteners torqued to spec. Often the torque spec specifies lubed or dry.
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You are right. It’s the same line of thinking only the dry vs lubed numbers seem to be settled science.

My question was more just one of curiosity, not specifically how tight should I tighten my shock mounting bolts or even one looking for a definitive answer.
 
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mrblaine said:
Simple method would be to see how much torque it takes to turn the Stover nuts before they bottom out and add that to your torque value. I am however, practically certain that an engineer will be along shortly to correct that since I've never seen it talked about anywhere.
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⬆️This engineer agrees with that engineer ⬆️ (you may disagree, but that's a compliment, Mr. Blaine ;))

Prevailing-torque nuts are, for practical purposes, constant-torque nuts. The hoop stress generated once the screw is completely through the nut doesn't change as you turn it, as long as it's not bottomed out. That hoop stress simply increases the load on the thread faces, and that load is directly proportional to the torque required to turn it, with the scale factor being the friction coefficient. Measure the free-spin torque and add it to the required torque, as Mr. Wizard suggested.
 
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Because I had some time this afternoon, I decided to begin a new episode of Project Farm.

I used a new grade 8, 1/2 - 13 bolt, and a new stover nut. Once the nut was fully engaged with the bolt, it took about 130 inch pounds (just under 11 foot pounds) of torque to turn it...

If someone double-checks my work, they may come up with different numbers because my smallest foot-pound torque wrench starts at 20, and my inch-pound torque wrench ends at 14 ft lb. But either way, it's good enough for shock bolts and at least as good as two ugga-duggas.
 
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Stinkbug said:
Because I had some time this afternoon, I decided to begin a single episode of Project Farm.

I used a new grade 8 1/2 - 13 bolt and a new stover nut. Once the nut was fully engaged with the bolt, it took about 130 inch pounds (just under 11 foot pounds) of torque to turn it...
Click to expand...

How much with anti-seize?
 
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mrblaine said:
How much with anti-seize?
Click to expand...

That would add an additional variable, keep me up at night and bring me right back to two ugga-duggas.

But if someone tried it, I bet they would be right back to the original torque spec of 74 pounds, with the anti-seize compensating for the stover or at least pretty close.
 
Stinkbug said:
That would add an additional variable, keep me up at night and bring me right back to two ugga-duggas.

But if someone tried it, I bet they would be right back to the original torque spec of 74 pounds, with the anti-seize compensating for the stover or at least pretty close.
Click to expand...

Not sure where you got that number but if I were to apply a torque value to those, it would be around 100 ft. lbs. Unless I'm mistaken somehow, those are grade 8 bolts in 1/2-20 which are gold zinc so considered to be lubricated or at least not dry.
 
  • I found the 74-lb number in the 1997 FSM for the lower shock mount. I stuck with that number in the absence of any good reason to go higher. I now think I am being given a reason to go up to 100 lbs on both the upper and lower bolts.
  • The grade 8, 1/2 -13 are the bolts and nuts that the guy that outboarded my shocks used
  • I did not understand that grade 8 good zinc-coated bolts are considered lubricated. I am wiser now, but I am unsure if that would reduce the 100 pounds mentioned above to 80ish to account for the lubricating effect of the gold zinc.
 
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Stinkbug said:
  • I found the 74-lb number in the 1997 FSM for the lower shock mount. I stuck with that number in the absence of any good reason to go higher. I now think I am being given a reason to go up to 100 lbs on both the upper and lower bolts.
  • The grade 8, 1/2 -13 are the bolts and nuts that the guy that outboarded my shocks used
  • I did not understand that grade 8 good zinc-coated bolts are considered lubricated. I am wiser now, but I am unsure if that would reduce the 100 pounds mentioned above to 80ish to account for the lubricating effect of the gold zinc.
Click to expand...
The factory lower shock bolt is 12mm coarse thread which has nearly the same minor diameter at the threads as 7/16-14. Slightly larger so the torque value can increase slightly to achieve a slightly higher clamp load.

The coarse thread bolts were included with the mounts and have long since stopped being used in favor of fine thread versions due to slightly more strength, slightly higher resistance to loosening, and the ability to use a high strength thread locking compound like Loctite 271 and a regular nut.

I am not a fan of thread deforming lock nuts. I've dealt with and seen far too many ruined fasteners when they are used.

1743256913422.png
 
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mrblaine said:
The factory lower shock bolt is 12mm coarse thread which has nearly the same minor diameter at the threads as 7/16-14. Slightly larger so the torque value can increase slightly to achieve a slightly higher clamp load.

The coarse thread bolts were included with the mounts and have long since stopped being used in favor of fine thread versions due to slightly more strength, slightly higher resistance to loosening, and the ability to use a high strength thread locking compound like Loctite 271 and a regular nut.

I am not a fan of thread deforming lock nuts. I've dealt with and seen far too many ruined fasteners when they are used.

View attachment 604530
Click to expand...

Thank you, that is the most helpful chart I have seen for torque values of the same size fastener under varying conditions (zinc plated, dry, lubed, etc.) to achieve the same clamping force. Prior to seeing this, I only considered dry or lubed conditions. Can you share a link so I can bookmark it for future reference?

I think my plan here is to increase the torque on my existing 1/2-13 fasteners to 100 (the k=0.17 column value of 90 + additional 10 for the stover) and call it a good. The next time I have the shocks rebuilt I can use the fine thread bolts.
 
Stinkbug said:
Thank you, that is the most helpful chart I have seen for torque values of the same size fastener under varying conditions (zinc plated, dry, lubed, etc.) to achieve the same clamping force. Prior to seeing this, I only considered dry or lubed conditions. Can you share a link so I can bookmark it for future reference?

I think my plan here is to increase the torque on my existing 1/2-13 fasteners to 100 (the k=0.17 column value of 90 + additional 10 for the stover) and call it a good. The next time I have the shocks rebuilt I can use the fine thread bolts.
Click to expand...

https://www.fastenal.com/content/feds/pdf/Torque-Tension Chart for A307 Gr5 Gr8 Gr9.pdf

I use it because it is handy and easy to understand and useful for me to compare other points of data. I have no idea as to whether I depend on it to build a spacecraft.
 
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