Bill N wrote:

> So why do we torque metric bolts to ft. lb. specs?  Why not to kilo newtons?
>

Torque is expressed in units of force multiplied by distance.
 (The distance being the length of the lever arm.)

In some cases( as on my cheapo torque wrench from Harbor Freight) the "metric"
approach results in torque specs given in meter-kilograms.  This is not really
correct because the kilogram is unit of mass, not force.  Of course under normal
gravity 1 kg has a weight of 2.2 lb (or in metric units, 9.8 Newtons), so the
force implied is actually equal to the weight of a kg.

Since the correct metric unit of force in the Newton, torque (in metric units)
should be written in Newton-meters  ( N-m).  This is the approach used by
physicists tho probably not yet by automotive engineers in the U.S.

In my Bentley (thru '91) I find torque specifications given in Nm and well as
ft-lb.

OK, more than you wanted to know.  Sometimes we physics teachers just can't help
ourselves.

Larry A.
Chicago