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MS21042 nut running torque

TASEsq

Well Known Member
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Just thought I would share my findings with others to make sure everyone else uses about the same running torque?

Please let me know if you are the same / significantly different!!

Setup was an AN3 or AN4 bolt held in a drill press vice which was clamped to the table so it couldn?t rotate. I then ran the nut onto the bolt so that about 1 thread was showing out the end (so full contact with but threads by the bolt). The scale was read while the nut was in motion, and the wrench was held at the end on the black knob.

Findings were (measured running torque):
AN3 / MS21042-3: 10 in/lbs
Photo here: https://photos.app.goo.gl/7x8RaqQewQXRXBj16

AN4 / MS21042-4: 24 in/lbs
Photo here: https://photos.app.goo.gl/sNossUFGPXjkcWfw7

As such on my click type torque wrench I would use as the wrench setting:
AN3: 38 in/lbs (28 + 10)
AN4: 109 in/lbs (85 + 24)

Look forward to some concurrence / discussion!
 
you must allow for running torque. if I remember correctly, my numbers were less than half of what you posted for nylocs.

edit: the nuts you are testing are not nylocs.

folks should remember the bolted joints,attachment fasteners and hinges are the most critical parts in the build. even more important than rivets.

good job to do the check.
 
Last edited:
AN 365 Elastic Stop Nut Retention Force

I have done a lot of testing of "retention" torque for the AN365 series hex nuts and following are the results.

AN365-3 = 5.0 in-lb
-4 = 9.3 in-lb
-6 = 41.4 in-lb

What I call the "tare" torque increases the torque specs to:

-3 = 20 to 25 + 5 = 25 to 30 in-lb
-4 = 50 to 70 = 9.3 = (approx.) 60 to 70 in-lb
-6 = 160-190 + 41.4 = (approx.) 200 to 230 in-lb

In general terms, if you torque to the high end of the range (+ a "skosh"), you will probably remain inside the allowable range.

Also, regarding reusing these fasteners - the retention torque goes way down (can you say 50%) on the second application. There are specs out there on the reduction of this value, down to the 5th reuse.

Note: Testing done with a purpose made 12" moment arm wrench, a .1 gram digital scale, at least 1 full thread showing past nylon insert, and the load at stiction being discounted.

Of course, as always YMMV

HFS
 
To avoid confusion when discussing details, it is always helpful to use the official nomenclature.
The measurable torque that exists while turning a fasten prior to a fastener bottoming out and beginning to tighten, because of a self locking feature, is referred to as prevailing torque. An alternative (but lesser used in aviation) nomenclature is running torque.
 
I also just tested some AN365 nuts and found the following:

AN365-1032A (AN3) = 3 in/lbs
Photo here:https://photos.app.goo.gl/oFMqBrDj1jF8AgGG7

AN365-428A (AN4) = 15 in/lbs
Photo here:https://photos.app.goo.gl/oFvmVyUwNBNjc8RG8

Section 5 also had the following comment:
?As an example illustrating the importance of determining the friction drag torque consider a new AN3 bolt and MS21042-3 all-metal
lock nut. Our tests showed an average friction drag torque of 14 in-lbs (your results may vary)?

So I reckon the 10 in/lbs is good for my HS bearing brackets - 38 in/lbs total.
 
You will find the torque to vary on different nuts from different manufacturers. I would not even be surprised to find small variations on nuts from the same manufacturer.
 
You will find the torque to vary on different nuts from different manufacturers. I would not even be surprised to find small variations on nuts from the same manufacturer.

And also variations between new unused bolts and bolts that have been previously used in a self-locking fastener.
 
Awesome - thanks all.

I was thinking I could just use the same value going forward but sounds like it might just be easier to do the nut up with the beam type wrench and measure the ?prevailing torque? with each nut, then finish with the proper calibrated click type.
 
Just more data points from two builds.

For AN3-365's I ended up adding 7 in pounds to the standard table. This was the pretty consistent average prevailing torque I measured during my Sonex build.

For the MS nuts used on the 14, I ended up adding 12 in pounds for the AN3 bolt nuts. There seemed to be more prevailing torque variance in the MS nuts - from 10 to 14 in pounds - so 12 ended up being my normal value.

I use my beam wrench to get these values. You can also see there is stiction when starting the nuts with the beam wrench. So, be sure and get the nut running and then take the constant value while the nut is turning.
 
I use my beam wrench to get these values. You can also see there is stiction when starting the nuts with the beam wrench. So, be sure and get the nut running and then take the constant value while the nut is turning.

Thanks Bob!
 
Running on torque

Be careful with running torque. Each nut is not the same......

That is why manufactures say "plus running torque" and not a set value.
 
Be careful with running torque. Each nut is not the same......

That is why manufactures say "plus running torque" and not a set value.

The torque value for a given fastener size being specified as a range vs a single value does a good job of accounting for that.

Add the prevailing torque value, to the value at the center of the range and you will be fine.
 
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