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### Bolt Threads Any Length Force to Strip Bolt Threads Formula and Calculator

Bolt & Screw Torque Charts and Equations

Force Required to Strip the Bolt Threads Any Length Formula and Calculator

The thread engagement length Le and the thread stress area ATS are directly proportional to each other. It is, therefore, very easy to compute stripping areas for engagement lengths other than nominal diameter, D:

When thread engagement is equal to thread diameter or when Le ≠ D

ATS' = ( Desired Le / D ) · ATS

Where

Le = Desired length of thread engagement (in., mm)
D = nominal diameter of the bolt (in., mm)
ATS = thread stress area (in2, mm2)

ATS
ATS' = Recalculated stripping area for a length of thread engagement greater to or less than the nominal diameter of the fastener (D) (in2, mm2).

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