Manufacturers' and technical manuals generally
information on measuring and marking tools. In this
specify the amount of torque to be applied. To assure
section we will cover the use of specialty measuring
getting the correct amount of torque on the fasteners,
devices such as torque wrenches, calipers, feeler
gauges, metal gauges, and squares.
the wrench must be used properly according to manu-
Use that torque wrench that will read about mid-
range for the amount of torque to be applied. BE SURE
THAT THE TORQUE WRENCH HAS BEEN CALI-
There are times when, for engineering reasons, a
BRATED BEFORE YOU USE IT. Remember, too, that
definite force must be applied to a nut or bolt head. In
the accuracy of torque measuring depends a lot on how
such cases a torque wrench must be used. For example,
the threads are cut and the cleanliness of the threads.
equal force must be applied to all the head bolts of an
Make sure you inspect and clean the threads. If the
engine. Otherwise, one bolt may bear the brunt of the
manufacturer specifies a thread lubricant, it must be
force of internal combustion and ultimately cause en-
used to obtain the most accurate torque reading. When
using the deflecting-beam or dial-indicating wrenches,
The three most commonly used torque wrenches
hold the torque at the desired value until the reading is
are the deflecting-beam, dial-indicating, and microme-
ter-setting types (fig. 5-1). When using the deflecting
beam and the dial-indicating torque wrenches, the
Torque wrenches are delicate and expensive tools.
torque is read visually on a dial or scale mounted on the
The following precautions should be observed when
handle of the wrench.
When using the micrometer-setting type, do
lock the grip and adjust the handle to the desired setting
not move the setting handle below the lowest
on the micrometer-type scale, then relock the grip.
torque setting. However, it should be placed
Install the required socket or adapter to the square drive
at its lowest setting prior to returning to stor-
of the handle. Place the wrench assembly on the nut or
bolt and pull in a clockwise direction with a smooth,
steady motion. (A fast or jerky motion will result in an
Do not use the torque wrench to apply greater
improperly torqued unit.) When the torque applied
amounts of torque than its rated capacity.
reaches the torque value, which is indicated on the
handle setting, a signal mechanism will automatically
Do not use the torque wrench to break loose
issue an audible click, and the handle will release or
bolts that have been previously tightened.
"break," and move freely for a short distance. The
Do not drop the wrench. If dropped, the accu-
release and free travel is easily felt, so there is no doubt
racy will be affected.
about when the torquing process is complete.
Figure 5-1.--Torque wrenches.