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Participant

Join Date: Mar 2007
Posts: 3

# Torque to Tighten an M8 Brass Nut

05/02/2007 10:28 PM

Dear all,

How much torque is required for tightening a M8 nut brass on M8 stainless steel bolt ? Can anyone advise a setting value or a reference handbook or link, pls.

To be honest, I dont know why they use brass nut on s/s bolt. It's been there for yrs.

Thanks & regards,

TaTa

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Guru

Join Date: Nov 2006
Location: OH USA
Posts: 549
#1

### Re: Torque setting to tightening a M8 brass nut?

05/03/2007 10:35 AM

You don't mention the thread pitch so I'll assume it is coarse (M8 x 1.25). The correct tightening torque for this combination with a dry brass nut would be about 110 in-lbs.

Brass nuts are commonly used on SST bolts for a couple of reasons. One is it prevents galling and seizure of SST to SST threads and (2) in the event of thread stripping, the brass nut will fail first. In that case, the brass nut can be removed and replaced and the SST bolt reused. This is commonly done when the SST bolt or stud is fixed to the assembly.

Participant

Join Date: Mar 2007
Posts: 3
#2

### Re: Torque setting to tightening a M8 brass nut?

05/03/2007 7:01 PM

Thanks a lot for sharing yout knowledge BlueStone. It's vey helpfull indeed.

Your assumption is correct which is M8x1.25.

I converted the 110 in-lb to approx. 12.5 Nm.

Once again, Thanks a lot.

Anonymous Poster
#3

### Re: Torque to Tighten an M8 Brass Nut

05/04/2007 12:02 AM

You can go this way. 0.6 x pitch x 3.142 x nominal dia ( in this case 8 itself) x no:of threads in the nut x (0.25 x shear strength of the nut you use). The 0.25 can be increased upto 0.5 depending on your application. If it is very critical keep it between 0.25 to 0.3, if it just used kinna normal application can raise the same upto 0.5. These values are perfect for any application. Lastly the answer you get with the formula above is the basically the shear off strength. Now you can drill down to your respective units whether metric or british accordingly. If still help is required please revert back.

Mr. Idiot always.

Guru

Join Date: Mar 2007
Location: City of Light
Posts: 3961
#4

### Re: Torque to Tighten an M8 Brass Nut

05/04/2007 12:22 PM

To Mr. Guest,

Your formula is wright and wrong at same time. The shear section depnds on the relative "strength" of the 2 materials. The factor 0.6 can go as high as 0.875 if the nut is less strong than the bolt. From the other side when shear occurs all threads are equally loaded since all are at/over elastic limit. The shear limit is usually 0.6 of elastic limit of material (in fact near to 3^-.5) with a 0.5 factor there is a high risk if any overload occurs. It is better to have a safety factor of 1.5. It should also be considered that usually the limit is set taking into consideration the dispersion of the tightening tool. If this is too big an overload can occur even at assembly.

Anonymous Poster
#5

### Re: Torque to Tighten an M8 Brass Nut

05/05/2007 1:39 AM

Yes Mr. Nick name,

I totally agree with you. First of all, the way I have put across seems to be confusion. In clarification to same, 0.6 was the root width ( In ideal case 0.875 as you said and close to 0.8 in precise applications). the 0.25 to 0.5 factor is the FOS ranging from 4-2. Hope I am clear while all that you have shared is also perfectly right.

Mr. Idiotalways.

Anonymous Poster
#6

### Re: Torque to Tighten an M8 Brass Nut

05/12/2010 3:35 AM

Any chance you could give us an example, I have plugged the data for an 8mm brass bolt in to these equations but don't seem to get a usable answer...

Here's the values I have used.

0.8 x 1.25 x Pi x 8 x 5 x (0.25 x 235x10^6)

Here's the link to the reference for brass data that I used http://www.vegasfastener.com/Brass.php

My application is brass nut on a brass bolt. Any assistance would be greatly appreciated.