If an adaptor or extension is attached to the square drive of a click-type torque wrench and this adds to its length, then the applied torque will be greater than the pre-set torque. A formula can be used to find what the preset-set torque should be in order to obtain the correct applied torque.
Here is the formula:
RS = Torque setting of the torque wrench.
A = Distance from the center of the square drive of the torque wrench to the center of the handle grip pull point.
B = Length of the adaptor from the center of the square drive to the center of the nut or bolt. Use only the length which is parallel to the handle. See figure 1
T = Torque desired. This is the actual torque applied to the fastener. Here is a typical problem: What should the setting be when ‘‘A’’ is 12’’, ‘‘B’’ is 6’’ and ‘‘T’’ is 30 Ib. ft.
Therefore 30 pound foot of Torque will be applied at the fastener when ‘‘RS’’ is 20 pound foot.
Note: If the torque wrench reads in pound foot, then ‘‘T’’ should also be in pound foot. ‘‘T’’ and ‘‘RS’’ should be in the same unit of measurement. ‘‘A’’ and ‘‘B’’ should also be the same unit of measurement.