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### Force Required Strip Bolt Threads Formula and Calculator

Bolt & Screw Torque Charts and Equations

Force Required to Strip the Bolt Threads Formula and Calculator

The amount of tension we can create in a bolt depends not only on the strength of its body but also on the shear strength of its threads. If we’re designing a nut or deciding how deep to make a tapped hole, we’ll want to be sure that the thread engagement length will be great enough to allow us to develop the full ultimate strength of the bolt. A broken bolt is easier to detect than a stripped thread, so we never want the threads to strip.

When thread engagement is equal to thread diameter or when L_{e} = D

Where

L_{e} = length of thread engagement (in., mm)

D = nominal diameter of the bolt (in., mm).

Equation 1

F_{St} = S_{u} *·* A_{TS}

where

S_{u} = ultimate shear strength (psi, MPa) of the nut or bolt materials

A_{TS} = cross-sectional area (in.^{2}, mm^{2}) through which the shear occurs for a length of engagement equal to D

F_{St} = the force (lb, N) required to strip that length of threads of a bolt or nut

Tensile force required to break the bolt

*Equation 2*

*F _{Ten} = UTS · A_{S} *

Thread Stress Area

Metric M Series Thread Stress and Shear Areas * *

Where:

*UTS* = ultimate tensile strength of the bolt material ( psi, MPa )

*A _{S}* = the tensile stress area of the bolt ( in.

^{2}, mm

^{2})

*D*= nominal diameter of the bolt ( in., mm )

*n*= number of threads per inch

*F*the tensile force required to break the bolt ( lb, N )

_{Ten}=If the computed F_{St} is greater than *F _{Ten}* your deign is adequate.

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Reference:

Introduction to the Design and Behavior of Bolted Joints Non-Gasketed Joints, Forth Edition

Founding Editor

L. L. Faulkner

Columbus Division, Battelle Memorial Institute,

Department of Mechanical Engineering

The Ohio State University

Columbus, Ohio