Thread Engagement Length

When the nut material is weaker than the bolt material

Dsmin: minimum OD of bolt threads (inch)
Enmax: maximum PD of nut(inch)
Sst: tensile strength of bolt material (pound/inch2)
n: number of threads per inch
As: tensile stress area of bolt (inch2)
Snt: ultimate tensile strength of the nut material (pound/inch2)
Ats: shear area of root of nut threads (inch2)
Le: length of engagement required to develop full strength (inch)

threadengagement2a.gif
threadengagement2b.gif
Le
Ats
As
Dsmin
Enmax
Sst
Snt
n

An Introduction To The Design and Behavior of Bolted Joints
Third Edition, John H. Bickford