Nut Thread Bending Factor
Nut Thread Bending Factor
(OP)
This is a late follow-up question to thread725-35222. I was wondering where values are obtained for dimensionless nut thread bending factor C3. The original post was for a steel to steel bolted connection, and recommended using .897. In my case, I have a steel bolt (grade 8), and 6061-T6 threaded plate.
I tried googleing and had no luck.
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I tried googleing and had no luck.
Just joined this forum, and think it's great.





RE: Nut Thread Bending Factor
C3 = 0,728 + 1,769 Rs – 2,896 + 1,296
for 0,4 < Rs < 1
or
C3 = 0,897 where for Rs ? 1
and
Rs = (τBM · ASGM)/(τBS · ASGS)
where
C3 is the correction factor for thread engagement length
Rs is the strength ratio
τBM is the nut shear strength
ASGM is nut thread shear area during axial loading
τBS is the bolt shear strength
ASGS is the bolt thread shear area during axial loading
Regards,
Cory
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RE: Nut Thread Bending Factor
Thanks for the formulas.
I have an application where some tapped 3/8" UNF holes in an aluminum plate got stripped out by grade 8 screws. My first thought was to increase tapped hole size in aluminum to 1/2" UNF. I performed the calculations, and for fun I performed again using 1/2" UNC. I determined that the 1/2" coarse threads can actually handle a higher load.
My calculations show that shear areas for nut and screw both increased in the coarse screw which is a good thing for my application.
Does this make sense?
Thanks!
RE: Nut Thread Bending Factor
Please disregard my last post. I found a mistake in my calculation and am re-evaluating. My nut shear area did not increase with the coarse thread.
Sorry,
ron
RE: Nut Thread Bending Factor
My question is however, when determining the maximum load that the nut can handle, should I base nut and bolt shear areas on the Le from Q=J*Le, where Q is the length of engagement required because of the difference in material strength.
I had always believed the first 5 to 6 threads are taking most of the load, so I would think using the smaller Le (not Q value) should be used.
I am also trying to determine whether to use coarse or fine threads for my application. From my nut (tapped hole)calculations so far, fine threads have more shear area as compared to coarse threads, but when I perform final calculation with the nut bending factor, the coarse threads end up being the stronger option (C3 is larger value for coarse thread).
Any comments?
RE: Nut Thread Bending Factor
I don't understand your Q equation. VDI 2230 uses the length of full thread engagement as its basis for maximum force to strip internal threads.
Regards,
Cory
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