wrench. These torque wrenches are all used in a
each time it is needed. A nut or bolt that is not
very similar manner.
torqued to the proper value may cause damage
To use the micrometer setting type, unlock the
to the component or equipment.
The proper procedure is to tighten at a
grip and adjust the handle to the desired setting
uniformly increasing rate until the desired torque
on the micrometer scale. Relock the grip. Install
is obtained. In some cases, where gaskets or other
the required socket or adapter to the square drive
of the handle. Place the wrench assembly on the
parts cause a slow permanent set, the torque must
nut or bolt and pull in a clockwise direction with
be held at the desired value until the material is
sealed. When applying torque to a series of bolts
a smooth steady motion. A fast or jerky motion
on a flange or in an area, select a median value.
will result in an improperly torqued unit. When
If some bolts in a series are torqued to a minimum
the torque applied reaches the torque value
value and others to a maximum, force is con-
indicated on the handle setting, the handle will
centrated on the tighter bolts and is not distributed
automatically release or "break" and move freely
evenly. Such unequal distribution of force may
for a short distance. The release and free travel
cause shearing or snapping of the bolts.
is easily felt, so there is no doubt about when the
Torque wrench size must be considered when
torquing process is complete.
torquing. The torque wrenches are listed accord-
The following precautions should be observed
ing to size and should be used within this
when using torque wrenches:
recommended range. Use of larger wrenches that
have too great a tolerance results in inaccuracies.
1. Do not use the torque wrench as a hammer.
When an offset extension wrench is used with a
2. When using the micrometer setting type,
torque wrench, the effective length of the torque
do not move the setting handle below the lowest
wrench is changed. The torque wrench is so
torque setting. Place the micrometer at its lowest
calibrated that when the extension is used, the
setting before returning it to storage.
indicated torque (the torque that appears on the
3. Do not use the torque wrench to apply
greater amounts of torque than its rated capacity.
dial or gage of the torque wrench) may be
4. Do not use the torque wrench to break
different from the actual torque that is applied
loose bolts that have been previously tightened.
to the nut or bolt. The wrench must be preset to
5. Never store a torque wrench in a toolbox
compensate for the increase when an offset
extension wrench is used.
or in an area where it may be damaged.
Occasionally, it is necessary to use a special
Torquing can be described as the twisting
extension or adapter wrench together with a
standard torque wrench. To arrive at the resultant
stress that is applied to the fasteners to secure
required torque limits, use the following formula:
components together. These fasteners can be nuts,
bolts, studs, clamps, and so forth. Torque values
for these fasteners are expressed in inch-pounds
or foot-pounds. Unless otherwise stated, all
Where:
torque values should be obtained with the
manufacturer's recommended thread lubricant
S = reading of setting of torque wrench;
applied to the threads.
T = recommended torque on part;
Torque values are listed in the appropriate
section of the applicable instruction manual. In
L = length of torque wrench (distance be-
case there is no torque specified, standard torque
tween center of drive and center of hand
values can be found in the Structural Hardware
grip); and
Manual, NA 01-1A-8, or in your particular air-
E = length of extension of adapter (distance
craft general information MIM. Regardless of
whether torque values are specified or not, all nuts
between center of drive and center of
in a particular installation must be tightened alike
broached opening measured in the same
place as L).
amount. This permits each bolt in a group to carry
its share of the load. It is a good practice to use
EXAMPLE: Recommended torque is 100
a torque wrench in all applications.
inch-pounds. Using a 12-inch torque wrench and
Using the proper torque allows the structure
a 6-inch adapter, determine reading on torque
to develop its design strength and greatly reduces
wrench.
the possibility of failure due to fatigue. One word
of caution--never rely on memory for torque
information, but look up the correct torque value
2-10
