Lesson 5/Learning Event
Micrometer or Clicker
The micrometer-type torque wrench, Figure 65, has a built-in micrometer at
the end of the handle where a specified torque can be set by turning the
handle. When the specified torque is reached, a loud click is heard. This
type torque wrench permits very accurate tightening of nuts and bolts.
Regardless of their type, most torque wrenches measure torque in foot-pounds
(ft-lb). However, some torque wrenches (mainly those used for more accurate
readings on smaller nuts and bolts) measure torque in inch-pounds (in-lb).
Twelve inch-pounds equal 1 foot-pound.
To convert foot-pounds to inch-
pounds, multiply the foot-pound by 12.
To convert inch-pounds to foot-
pounds, divide the inch-pounds by 12.
Example of converting foot-pounds to inch-pounds:
75 foot-pounds x 12 inch-pounds = 900 inch-pounds.
Example of converting inch-pounds to foot-pounds:
1,260 inch-pounds 12 inch-pounds = 105 foot-pounds.
Torque wrenches are issued in several sizes; they may have a 1/4-, 1/2-, or
3/4-inch square drive to receive socket wrenches, and the capacity may range
up to 600 foot-pounds.
SELECTING A TORQUE WRENCH FOR A SPECIFIC JOB
Before selecting a torque wrench for a job, note the torque specification.
Then select and use a torque wrench that will read about midrange for the
specified torque. For example, a typical 1/2-inch drive micrometer torque
wrench measures from 30 to 200 foot-pounds.
It would be the best torque
wrench for a job requiring about 100 foot-pounds of torque.
3/8-inch-drive torque wrench reads from 15 to 100 foot-pounds. A 1/4-inch-
drive torque wrench measures from 30 to 300 inch-pounds.