I have 3/8 - 16 grade eight bolts with nyloc nuts. What torque value?

 

My guess would be to determine the initial (loose) torque that the nyloc nut adds to the equation. Then add that to the torque specified for the 3/8-16 grade 8 bolt (my specs say it is 50 ft.-lbs.).

But knowing that as nyloc nuts wear, they become "looser", that may be faulty thinking......

Good luck,
Plasticman

 

You beat me to it, John. This is what I was going to suggest. It seems like a reasonably scientific approach.

Jim

 

http://www.practicalmachinist.com/vb...nylock-176110/

 

Thank you. I'll use 47 - 50 ft-lbs.

 

Update

The bolts are identifiable as grade 8. The nuts have no ID and Nyloc nuts come in grade 3, 5, and 8 but I don't know what I have.

I couldn't achieve 45 ft lbs on any of them, so I backed them all off and settled for 30 ft-lbs. Hopefully I didn't damage any of the fasteners.

 

I am making some assumptions here, but I "assume" that you are using grade 8 bolts for a reason (critical application that requires the higher strength) and I had "assumed" that the nyloc nuts that you first posted about were grade 8.

Since nuts typically are not "grade marked" (never know exactly what you have), and they might be used in a critical location, best to get the correct nuts for the job. It is useless to use a grade 8 bolt with a lesser grade nut (the weakest link is the nut), and bolt clamping force is obviously less, if forced to lower the tightening torque due to a weaker nut.

Since you could not achieve minimum grade 8 torque (nut was stressed beyond it's material capability), the nuts have been damaged (maybe a little, maybe a lot).

In other words, if it is a critical application, I would get the correct grade 8 nuts.

plasticman

 

What are you using these bolts for? If they are being used for strength or a critical connection, it may be simpler just to use high strength bolts and some blue threadlocker.

 

Coming from my technical / mat'l testing background : in equivalent grades - nuts do not fail.
Bolts will fail before nuts.

If you could not reach the req'd torque - something was yielding (failing) - you have overstressed (stretched) one of the components and degraded it's strength capability.

It is unusual to be using to be using Nylock type nuts for a high tension application.
Threaded fasteners depend on tension to prevent them coming loose.
Nylock nuts would be applicable for places where you anticipate something losing it's clamping tension and therefore becoming loose.

 

3/8 16 thread usually torques at 35 lb ft. The nylock doesn't fit into the torque reading of the equation for me. It is used to keep the nut from allong off if the nut loosens on the threads. That's just my opinion, I could be wrong.

 

These were given to me by the fellow who welded up the removable transmission crossmsmber. They are used to bolt the new flanges together.

The SAE chart that I found online says Gr 8, 3/8 - 16 bolts take 47 ft-lbs.

 

I was thinking grade 5. For grade 8 you are spot on at 47. I still take the nylock out of it because you overcome the nylock resistance before you reach torque with the nut.

 

From airresearch.com
airresearch.com/Toolbox/NylockNut.doc



Nyloc is a registered trade name of Forest Fasteners.

A Nylock nut resists turning. Usually nuts are free spinning, but Nylock nuts have a plastic patch that causes resistance to nut turning. This resistance is called "prevailing torque". Prevailing torque is the torque required to turn the nut. None of the prevailing torque goes toward tightening the bolt.

Nylock nuts fall within a group of nuts called 'lock nuts" Lock nuts come in all types and sizes. Typically there are the "Nylock" or elastic stop nuts, and the "all-metal" lock nuts.

The rule of thumb is to add the prevailing torque to the torque value when applying torque to a Nylock nut. This is because the prevailing torque doesn't contribute to bolt tightening. It is just friction that needs to be overcome.

For example, a Grade 5 1/4-28 bolt in tension lubricated zinc plating, with a torque of 10.5 lb. ft. produces a clamping load of 2,511 pounds.

If we use a use a Nylock nut that takes 2 lb. ft. of torque to turn, then 2 lb. ft. of torque is used in turning the nut leaving only 8.5 lb. ft. for bolt tension. Our clamping load is reduced to 2,009 pounds.

If, however, we take our original torque of 10.5 and add the 2 that the Nylock requires and set our torque wrench to 12.5, our clamp load is 2,511 pounds. The same as it was without the nylock.

You can use your torque wrench to measure Nylock nut torque and then add this value to the bolt's required torque.

Prevailing torque calculation should be done with your nut and your bolt using your thread lubricant. Published prevailing torque charts may give you an idea of how much torque is used up by the nut's locking feature, but in actual conditions, the results will vary. There is an interaction between the bolt threads, nut locking feature, and the thread lubricant (whether liquid or plating) that makes each prevailing torque calculation unique.

--exceptions to this rule----

Usually you wouldn't add prevailing torque to the torque value published by the equipment manufacturer. The equipment manufacturer has already done this for you. For example, propeller bolts use elastic stop nuts (prevailing torque nut). The propeller manufacturer is aware of this. So just go ahead and use the published torque values.

If you use a different nut or a different thread lubricant than what the manufacturer specifies, then the proper torque is unknown.

 

just tighten them by feel, for where you are using them. no torque needed! Turn with a normal size wrench till tight and then just a little bit more (a snug)! Grade 8 really??? but what the heck, you have them so use them! With inferior nuts, you don't want to torque anyways, which is stretching a bolt technically, so just snug them good or you will strip or gall the hardware. $hit sounds like you have 4 bolts per flange.

If you still can't sleep, then check them next month!

NUTS!

Oh by the way, did you go to the gorilla school of throwing a shifter where grade 8 is the thought to keep that tranny tailshaft where you put it? you don't have to answer that one!

DOUBLE NUTS!

 

This is the reason why I stay off the forum - people complicate the living dung out of the simplest tasks.

WHY DO YOU NEED GR 8 BOLTS ??
Because some unknowing soul gave them to you who doesn't know any better ?

Put in some GR 5 bolts tighten them up and move on. Sheesh !

 

Because it is a frame crossmember that has been modified for a removable section, he is going to make that crossmember strong!

50% or more on this forum would do the same thing!

 

Certain of you dopes should reread post #6. Reread the third sentence until it sinks in. For some of you it might require ruminating over it for a few hours.

If you still don't get it, that third sentence means that I have "moved on" a long time ago.

Expected this thread to end after post #6, but some of you insist on beating dead horses.

HAND

 

Pardon us for trying to help.............and I think you mean post #6, but then again.....

Plasticman

 

Sorry you thought I was talking to you. You posted some good information. You're right about post #6, and I edited accordingly.

You see, even us smart guys make mistakes sometimes.

 

Also please realize that this whole time I know it's you! And you are one of the smarter ones and definitely more knowledgable guys!!!!! Just having fun with you!

No hard feelings I hope!

But it was your post #11 after #6, that made me do it, at least that is what story I will stick to!:chee rs: