Related Resources: calculators

### 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 Le = D

Where

Le = length of thread engagement (in., mm)
D = nominal diameter of the bolt (in., mm).

Equation 1
FSt = Su · ATS

where

Su = ultimate shear strength (psi, MPa) of the nut or bolt materials
ATS = cross-sectional area (in.2, mm2) through which the shear occurs for a length of engagement equal to D
FSt = 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
FTen = UTS · AS

Where:

UTS = ultimate tensile strength of the bolt material ( psi, MPa )
AS = the tensile stress area of the bolt ( in.2, mm2 )
D = nominal diameter of the bolt ( in., mm )
n = number of threads per inch
FTen = the tensile force required to break the bolt ( lb, N )

If the computed FSt is greater than FTen your deign is adequate.

Related:

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