**Related Resources: calculators**

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

**Torque Design Menu
**

**Bolt Preload Equations**

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

*T _{3} = ( d + b ) / 4 µ_{2} p_{B}*

With the coefficient of friction, *µ _{2}* between the nut or bolt head washer face and the joint the friction load is:

*Equation 2
f _{L} =
*

*µ*

_{2}p_{B}

Where:

*T _{3} *= Torque to overcome friction in-lbs, mm-N

*= friction coefficient*

µ

µ

_{2}*= inner diameter contact surface, in, mm*

d

d

*b*= outer diameter contact surface, in, mm

*p*= axial force

_{B}

Figure 1 Nut or bolt head friction force

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

Related:

- Bolt Elongation by Turn Formulas and Calculator
- Bolt Elongation by Stress Formulas and Calculator per. MIL-HDBH-60
- Torque Wrench Adapter for Reduced Arm Equation and Calculation
- Torque Clamp Force Calculator
- Stud Preload Calculator
- Bolt Preload Tension Equation and Calculator
- Bolt Preload Tension Force Calculator
- Torque vs Tension Bolts Table Chart SAE J429 Bolts
- Bolt Multiple Diameters Change of Length Under Axial Force Formula and Calculator