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Operating Instructions • Warning Information
General Information...
What is a Torque Wrench?
A torque wrench is a precision measuring instrument much the same
as a micrometer, vernier calipers or any other ac cu rate measuring
instrument. Its purpose is to mea sure or limit the amount of torque
being applied at a given point.
What is Torque?
Torque is a twist or the resistance to rotation. When used in reference to
a bolt, torque is the resistance to turning of the bolt or nut.
How is Torque Measured?
Torque is based on the fundamental law of the lever – that is – force
times distance equals the torque or twist around a point.
Torque is most commonly measured in foot pounds or inch pounds. For
example: If a 1-pound force is applied 1 foot from the center of the
bolt, the resulting torque de vel oped would be referred to as one foot
pound of torque.
1 FT.
T
Torque 1 Foot Pound
If the distance is measured in inches, the resulting torque would be
referred to as twelve inch pounds of torque.
12 Inches
T
Torque 12 Inch Pounds
What does Torque do to a Bolt?
Applying the exact amount of torque to a nut or bolt in duc es the correct
amount of tension or elongation in the bolt that is necessary to hold the
parts together. Fur ther more, by ap ply ing the correct amount of torque
specified to a bolt, the dan ger of distortion to the part or adjoining parts
is elim i nat ed.
What is Tension?
Tension is straight pull and is measured in pounds. Torque wrenches
are at times referred to as tension wrench es. This is not true. Wrenches
that are de signed to measure or limit the amount of torque applied to a
nut or bolt are definitely torque mea sur ing instruments.
Importance of Accurate Torque
If a nut or bolt is not tight ened enough, it will eventually work loose and
drop off. At the other extreme, if too much torque is applied, the nut or
bolt will very likely snap off. In either event an obvious fail ure occurred
due to improper torquing of the fastener.
9701A/9702A/9703B: Operating Manual
90º
1 LB.
90º
1 LB.
Metal is an Elastic Material
Every type and grade of metal has a definite limit to which it can be
safely stretched or stressed. This is defined as the elastic limit of the
material.
Design engineers must con sid er many things in se lect ing the correct
fastener. As engines, transmissions, and ma chines become more
com plex, their design is such that max i mum efficiency is de pen dent
upon applying the correct amount of torque to the fasteners that hold
component parts to geth er. After the cor rect fastener and material has
been cho sen the design en gi neer establishes the exact amount to
torque to be applied. This torque specification will induce a stress or
elongation of the bolt of approximately 60-70% of its ultimate elastic
limit.
In the case of aluminum and other soft metals, their ul ti mate strength
often dictates the correct amount of torque rather than the strength
of the steel bolts holding them to geth er. Soft materials in joints, such
as gaskets, also tends to reduce the amount of torque that normally
would be ap plied. Too much pressure would damage or distort the
ma te ri al.
How Adapters Affect Torque
To understand why certain types of adapters and extensions change
the amount of torque delivered at the bolt head, it should be
remembered that the amount of torque pro duced on the bolt is the
result of the amount of force applied and the length of the torque
wrench, plus the length of the ex ten sion or adapter. Remember
the torque law? Force x dis tance = torque. However, when special
accessories are used that add length to the torque wrench, the setting
no longer reads true and corrections must be made to compensate for
any added length. Adapters or extensions may be used with a torque
wrench for many reasons:
1. To adapt torque wrench to special fittings or ap pli ca tions; or
2. To increase or multiply torque past the capacity of the wrench; or
3. To torque fasteners in hard to reach locations.
How to Compute Torque
If an adapter is attached to the square drive of a torque wrench, the
wrench will not give the actual torque in di cat ed by the setting of the
handle. A simple formula how ev er, al lows you to figure out what the
setting should be to deliver a predetermined amount of torque at the
end of any adapt er to the fastener.
Here is the formula:
A
C = D x
(A + B)
NOTE: The above formula applies only to torque wrenches.
D
B
3
C
A
04/05/16
