Use of Crow Foot Spanner Adapters with Torque Wrenches

The use of a crow foot spanner adapter will effectively lengthen the lever arm of a torque wrench. The amount of torque applied to a fastener is increased as the torque wrench lever arm is extended, therefore the torque wrench setting must be adjusted in order to achieve the correct tightening torque.

Before tightening a fixing using a crow foot spanner adapter, measure the normal length of the torque wrench from the centre of the drive square to the centre of the handle (dimension L1). Fit the crow foot spanner adapter to the torque wrench as shown below. Measure the extended length of the torque wrench from the centre of the crow foot spanner head to the centre of the handle (dimension L2).

Use the following formula to calculate the correct torque wrench setting to achieve the required tightening torque.

M1 = M2 x L1 / L2	Example
M2 is the required tightening torque to be applied	90 Nm
L1 is the normal length of the torque wrench, measured from the centre of the drive square to the centre of the handle	300 mm
L2 is the extended length of the torque wrench, measured from the centre of the crow foot spanner head to the centre of the handle	325 mm
M1 is the calculated torque wrench setting	83 Nm