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Bolt Head Friction Torque Formula and Calculator per. MIL-HDBH-60

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Bolt Head or Nut Friction Torque Formula and Calculator per. MIL-HDBH-60

Friction between the nut, bolt head or washer may need to be determined as part of specifying an accurate fastener torque.

Preview Bolt Head or Nut Friction Torque Calculator

Assuming the force is applied midway between the nominal diameter, d, and the washer face diameter, b, torque to overcome nut or bolt under head friction is:

Equation 1
T₃ = ( d + b ) / 4 µ₂ p_B

With the coefficient of friction, µ₂ between the nut or bolt head washer face and the joint the friction load is:

Equation 2
f_L = µ₂ p_B

Where:

T₃ = Torque to overcome friction in-lbs, mm-N
µ₂ = friction coefficient
d = inner diameter contact surface, in, mm
b = outer diameter contact surface, in, mm
p_B = axial force

Figure 1 Nut or bolt head friction force

Military Handbook, Threaded Fasteners - Tightening to Proper Tension MIL-HDBK-60

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