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Specifying Screw Torque

Specifying Screw Torque

Specifying Screw Torque

I am looking at somebody's notes in which they specify bolt torque as 75ft*lb. I am used to saying 75ft.lb. On SolidWorks drawings, I go 75_FT.LB, so that specifications like 25_OZ.IN will not be confusing. When I did this, I did not think to do 25IN.OZ.sadeyes

Is there an official standard for this that applies to process instructions and drawings?


RE: Specifying Screw Torque

A ft.-lb. is a unit of energy. Torque is given in lb.-ft. to prevent confusion.

RE: Specifying Screw Torque

ft.lbs or lbs.ft ... there's no difference.

Nm is a unit of energy ... would you use mN for torque ?

the units of the two (energy and torque are the same), the difference is found in the words describing the value ...

The object impacted with an energy of 100 ft.lbs (have to admit lbs.ft sounds better).

The bolt was tightened to a torque of 100 ft.lbs.

another day in paradise, or is paradise one day closer ?

RE: Specifying Screw Torque


I like to throw the dot in there for the precise reason you indicate, N.m=m.N.


RE: Specifying Screw Torque


Should Cosmos Users be Licensed? is an interesting discussion about someone who does not does not understand torque and energy.

I wonder where pkellner has got to?


RE: Specifying Screw Torque

My experience is that a rigid adherence to an arbitrary nomenclature leads to errors. "Everybody knows" that you use ft-lbf for energy and lbf-ft for torque leads to someone who isn't in on the joke using the "wrong" one and some of his readers being confused.

This is much like the air compressor industry using the term CFM (or CmM) without defining terms. As someone who works with compressors in industrial-gas service, the suction pressure of the compressors I work with often is orders of magnitude higher than atmospheric pressure. When air-compressor guys are looking for an industrial compressor they often specify "suction CFM" which only has meaning if the suction pressure and temperature are known and constant. The only way to solve this problem is to define your terms every time. I find it quite tedious to specify the pressure and temperature base I am going to use in each particular paper, but I still do it and have found that many people reach better conclusions because I've removed the ambiguity.

As to drawing annotations, I would pick a style, define it in the notes, and stick to it.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Specifying Screw Torque

knowing an alternative meaning for "CFM" ...

another day in paradise, or is paradise one day closer ?

RE: Specifying Screw Torque

Is it N.m or N·m?

Suggest using using energy units such a j to distinguish them from torque.

mN is short for milli-newton, while Nm might be mistaken for a nautical mile (nm) or a nano-meter (nM). Suggest using the dot rather than the period to multiply units. Not sure what purpose the underscore serves.

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