[ChrisBennet]

This is excerpted from some Raceware information. As you can see my memory was faulty (about the 80%). Sorry about that. Hope you find this as interesting as I did.
-Chris
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Torque Friction & Fasteners
(2nd page)

When you use a torque wrench to install a threaded fastener, the wrench is
actually used to apply and measure a force. The force is designed to
PROPERLY tension the fastener so it can perform it's job properly. If the
fastner is under or over tightened, it will prematurly loosen or fail.
Torque wrenches do not measure TENSION, they measure TORQUE. In the case of
a threaded fastener, torque is the radial force applied to overcome
friction in the threads and to streach or tension the fastener.

In quality threaded fasteners as much as 80% of the torque applied to
tighten them is used to overcome the friction in the threads. Only about 20%
of the force is used to actually tension the fastener. That means that any
change ins the FRICTION has DRAMATIC effect on tension. All quality
fasteners have specific installation instructions that dictate what
lubricant if any should be used when tightening the fastener. Lubricants
such as motor oil, anti-seize, moly lube, cam lube, STP(tm), ect, ALL have
different friction characteristics.

USING THE WRONG LUBRICANT CAN CHANGE THE THREAD FRICTION BY AS MUCH AS
30%, CAUSING A FASTENER TO BE IMPROPERLY TENSIONED.

Thread design and pitch also have a great effect on Torque and Tension.
Fine threads exert a greater tension on a fastener for the same amount of
Torque applied. This is because of the angle on the threads is smaller and
therefore the 'wedge" effect is greater. Thus if you tighten a fine thread
fastener to the same torque as a coarse thread fastener, the fine thread
fastener will have a higher tension, and clamping force. (clamping force is
the force created by a fastener that holds two or more parts together.) Due
to the difference in friction and "wedge" effect, fine threaded fasteners
are often tightened to a LOWER torque the coarse threaded fasteners, to
prevent over-tightening and failure.

Friction in a threaded fastener assembly is effected by many variables
including but not limited to: thread design, thread pitch, lubricant,
smoothness of surfaces, if a washer is used or not, LENGTH of thread
engagement, and fastener design, (i.e. a bold verses a nut), just to name a
few. When a bolt is tightened into an existing hold like a block or head
installation, friction is present at BOTH the threads and the bolt head. The
length of the thread engagement effects friction and torque. A nut has
considerably shorter, (in most cases), thread engagement than a bolt.
Therefore it is not necessary or desirable to tighten a nut to as high a
torque as a bolt, because the nut has less friction to overcome to
properly tension the fastener.