Technical data

13773-001
20-60
Page 1130 Nov 2000
B. Calculating Torque
To assure an accurate torque measurement, a smooth and even motion must be applied. Whenever a
bolt is torqued on the head side instead of torquing the nut, additional resistance (friction drag torque)
may occur due to the friction of the shank during rotation. This could result in an under-torqued fas-
tener. The value (friction drag torque) observed from the torque wrench indicator during the initial tight-
ening phase of the bolt (before seating of the bolt has been accomplished), must be added to the
torque value given in the specified torque table. When checking friction drag torque, use a torque
wrench which allows the friction drag torque to fall in the middle of the overall range of the torque
wrench. When using lock-nuts, the friction drag torque (from locking device) must be added to the
specified torque value.
When using a torque wrench with an adapter that changes the distance from the torque wrench drive
centerline to the adapter centerline, compensation must be made for the extra leveraged gained. New
torque specifications must be calculated before the wrench is used. To calculate the new torque speci-
fications, use the following formula.
(1) Requirements for Calculating Torque
(a) When selecting a torque wrench, select one that has the required torque specification in
the middle of the overall range of the torque wrench. When lower torque specifications are
called out, always use an inch-pound torque wrench or a smaller foot-pound torque
wrench. Use only calibrated torque wrenches that have been certified.
(b) Calibrate the torque wrench and recheck calibration frequently to assure accuracy.
(c) Thoroughly clean and dry all threads and fasteners prior to torquing.
(d) Torque only to the specified range; stopping instantly at the correct torque.
(e) When using a torque wrench adapter be certain to allow for the additional extension length
when torquing.
(f) Sheet metal screws and screws tightened to nutplates should be tightened firmly.
(g) Always start the nut or bolt by hand prior to the torquing process.
COMPOSITE STRUCTURE
Torque Specifications For FINE Thread Hex-head Tension And Shear Bolts, Or Any Bolted
Structure With Combinations Of Composite And Metallic Parts
Thread Size
Inch Pounds Nm
Minimum Dry
Torque
Maximum Dry
Torque
Minimum Dry
Torque
Maximum Dry
Torque
10-32 15 20 1.7 2.2
1/4-28 25 30 2.8 3.3
5/16-2450605.56.6
3/8-24 80 95 8.8 10.5
7/16-20 150 170 16.5 18.7
1/2-20 220 245 24.2 27.0