Which one is correct, in-lbf. or in-lbs., or in-lb.

[APH]

Guys,

Any idea?

APH

 

[israelkk]

In-lbf is the correct one which is force multiplied by displacement meaning energy/work or moment/torque. The others are just length unit multiplied by mass which has no meaning.

 

[byrdj]

my 2 cents
I've seen torque expressed as in-lbs, but work as in-lbf.

 

[jsummerfield]

SI units differentiate mass and force.

In text documents I would write the word inch-pound. My data sheets usually include a pull-down menu with available units.

Do not add the letter "s" to indicate plural units -- inch not inches, pound not pounds, lb not lbs. There is a nice guideline in the Fundamentals of Engineering handbook in the earlier chapters.

John

 

[zekeman]

in-lb is a unit of energy or work. If you want moment or torque it should be expressed in lb-ft.

 

[IRstuff]

The question is what are you trying to express? lbf is a unit of force, while lb is a often used as a unit of mass.

TTFN

 

[APH]

I'm trying to specify torque requirement on screws.

Thanks
APH

 

[TheTick]

In school, we used lbf and lbm to help avoid confusion between mass and force in the English system. I still do this.

The worst offenders, however, are the ones who dare to use m·kg or cm·g for torque!

"When everyone is thinking alike, no one is thinking very much." --Eckhard Schwarz (1930--2004)

http://www.EsoxRepublic.com

 

[JStephen]

Any one of the three. I haven't checked, but I'll bet my torque wrench doesn't show "lbf" on it, and you'd be writing it for the people doing the tightening.

Usually, the application will indicate whether the pounds are mass or force, and where you're specifying a torque, nobody's going to confuse it with mass.

Whether it's in feet or inches is immaterial. Work or torque can be expressed either way.

Gripe of the day: After learning the SI system over and over all through school, I discover all these foreign countries that use the metric system are giving stresses in kilograms per square centimeter. So much for SI.

 

[IRstuff]

Why is that problem? cm is an official prefix of the SI system:

http://physics.nist.gov/cuu/Units/prefixes.html

TTFN

 

[CoryPad]

The problem is using a mass unit (gram or kilogram) instead of a force unit (newton!!!!!).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TheTick]

It's a problem not because of the cm, but because kg is a unit of mass, not stress.

 

[TheTick]

D'oh! I meant kg is mass, not force.

 

[JStephen]

Actually, they mean kg-f, doing the same thing with kilograms that we do with pounds, using as units of both force and mass. Which is "metric", but not SI. Probably dates from 100 years ago, too. Proper units would be MPa. You'll also see units from cgs system still in use, which is also metric, but not SI.

 

[sreid]

My "vote" is for lb-in for torque.

 

[EnglishMuffin]

I always distinguish between lbf and lbm (I never leave off the "f" for force and sometimes add the "m" for mass)- just the way I was trained, but it also prevents confusion. I also agree with zekeman - force first for torque, displacement first for work/energy. So for torque it should be lbf-in or just lbf in. But an awful lot of people either don't know or don't care about the sequence distinction.

 

[gearguru]

JStephen,
MPa = Newton per mm square, it is the unit for stress or pressure.
kgf was used to make clear that we were talking about force (=9.81 N) not that long ago - say 20 years or so.
It was mostly this confusion what finally initiated establishing the Newton as a unit of force.
The lbf and lbm should be used to show what are we talking about. But they are not...

 

[JStephen]

I meant the practice of using kg/cm2 probably started 100 years ago, not that it was abandoned then. I know that it is STILL used by various steel mills. It may be shown as kg-f rather than just kg, but the intent is clear in either case.

It appears the SI system dates from 1960, based on a quick web search. When I started college in 1979, it was in use, with no suggestion that it was new.

 

[jsummerfield]

My only recent use of kg/cm2 was on a Pemex project. Most international projects use kPascal for pressure.

John