BOLT TORQUE K FACTORS CHART

Reference values for bolt torque K factors are given in the following bolt torque K factors chart. Use these values in case no information available from bolt manufacturers and suppliers for bolt K factor values.

Bolt Condition K
Nonplated, black finish  0.30
Zinc-plated 0.20
Lubricated 0.18
Cadmium-plated 0.16
Source : From Shigley's Mechanical Engineering Design [Ref 3] page 427


Following chart gives most common methods of preload application to bolt and their approximate accuracies.



Bolt Tension Measurement Method Accuracy   Bolt Tension Measurement Method Accuracy
By feel ±35% Computer-controlled wrench  
Torque wrench ±25% - below yield (turn-of-nut) ±15%
Turn-of-nut ±15% - yield-point sensing ±8%
Preload indicating washer ±10% Bolt elongation ±3−5%
Strain gages ±1% Ultrasonic sensing ±1%
Source : From Machinery's Handbook [Ref 2] page 1526 and NASA Fastener Design Manual (NASA-RP-1228) page 18

Note: Bolt Tightening methods using power drivers are similar in accuracy to equivalent manual methods.


Reference:
  • Oberg.E , Jones.D.J., Holbrook L.H, Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc. , pp 1521 - 1537
  • Budynas.R , Nisbett.K. (2008) . Shigley's Mechanical Engineering Design . 8th edition.  McGraw-Hill
  • Barrett T.R. (1990), NASA - RP - 1228, Fastener Design Manual