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# Need Torque Spec for Metric Class 9.8 through 12.9...

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## Need Torque Spec for Metric Class 9.8 through 12.9...

(OP)
So while our technical committee is drafting an internal standard, we need to have a ready made torque spec, available to the world. All of our work is done with metric fasteners. We use everything from black alloy, to blue dyed, with sizes ranging from M12 down to M1. I would need to cover button head, flat head, and socket head cap. I've seen both DIN and ISO fasteners.

Since I'm not a member of any technical societies, I was wondering if anyone can at least point me to a suitable standard? Apparently, we have quite an extensive library, somewhere, but I don't do spec research, so I'm not really sure where to start.

Thanks in advance.

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

Torque is about as accurate as the coefficient of friction between the mating parts, so I don't see the interest for such a table.
However, with the equation T = k F d (and multiply by 0.75/0.90 for temporary/permanent connections), with F the max. tensile force the bolt can transmit (by effective diameter and class) it should be easy to make a simple spreadsheet. Again, it is only as effective as your friction values...

Also, I haven't seen any 9.8 bolts, my table goes from 8.8 to 10.9 .

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

(OP)
I am very familiar with how to find torque. That wasn't the question.

This is a spec to be specified on all designs, so that we have a set of values that can be easily referenced. I'm not interested in idealistically dictating to anyone, how they should know how to use both a spreadsheet, and a torque wrench. I do not want to deal with non-conformance, post-fabrication. And seeing that I am a primary in this task, dealing with any such issues that arise, should be as least time consuming as possible.

There's plenty of reason to have tables. The listed values for clean, dry, and lubricated torque values are still plenty accurate, for most kinds of work, in a "normal" operating environment.

At the very least, I'd even accept someone telling me what Machinery's Handbook specifies as their basis. I'd look myself, but I'm currently holed up working from home, like most of the country...

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

(OP)
The raw information is not what I'm looking for. I'm looking for source documents. There is no way that I can call out a worksheet or an internet page in an engineering drawing, manufacturing spec, or inspection control document.

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

Manufacturers' data may reference source documents. It seems 8.8 and 9.8 are treated equally.

Ted

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

(OP)
When one uses manufacturer specific fasteners, one references manufacturer specific documents for those products. When one uses NAS or Mil-Spec, on references those standards. For everything else, there needs to be a common "catch all". This is very common for general design practice.

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

Hi
Check this link out it references BS EN 898-1

https://roymech.org/Useful_Tables/Screws/Screw_loa...

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

Oh I should of added it doesn’t give torque values though but gives proof loads etc and that’s because torque values are not accurate as some others have already pointed out.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

#### Quote (solid7)

The raw information is not what I'm looking for. I'm looking for source documents. There is no way that I can call out a worksheet or an internet page in an engineering drawing, manufacturing spec, or inspection control document.

I doubt you're going to find reliable sources like standards for this, as torque for indicating pretension is about as useful as an amish electrician, however some tool catalogs do have those tables.
Here's one for example from the 2008 Facom catalogue.

https://files.engineering.com/getfile.aspx?folder=... (CoF = 0.10)
https://files.engineering.com/getfile.aspx?folder=... (CoF = 0.15 and 0.20)

I do find it remarkable that you won't put a table with raw data on your drawings, however you are willing to put a torque/bolt size relationship on them if it comes from a reliable source. Do you take all or at least some other factors into consideration like bolt length, relative stiffness or base material, ... ?

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

solid7,

Metric fastener grade numbers actually specify ultimate and yield strengths. You can look up the standards and plug these into the equations recommended above.

If you create your own spreadsheet tables, as recommended above, you know what assumptions went into your screw torques. Lubrication? Re-use? Strength of the tapped holes? You need to state those assumptions clearly. The time comes when your table is not functional, and you have to work out the torque from first principles, and clearly document it.

Before you create your table, go down to your shop and inspect the torque drivers. If your torque tools are calibrated in lb.in, specify lb.in. You are the engineer with the spreadsheets. You do the unit conversions.

--
JHG

### RE: Need Torque Spec for Metric Class 9.8 through 12.9...

solid7,

I have one more thought about your own table. I generally set the friction coefficient k=0.2 for non-lubricated and k=0.15 for lubricated screws. This is the weak link in screw torque calculations. You can test your screw torques and work out a practical friction coefficient for your shop, with your fasteners and your work conditions. This makes your torque tables more accurate and reliable.

--
JHG

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