Unified Inch Screw Thread (UN UNC UNF UNEF) – Thread Strength

Tensile stress Area:

Tensile strength of externally threaded part:

Minimum thread shear area for internal threads:

Minimum thread shear area for external threads:

Shear strength of internal threads:

Shear strength of external threads:

The thread tensile stress area are used for the purpose of product acceptance computations.

Thread shear areas are geometric minimum values. Shear (Thread Stripping) strength of screw threads under load are dependent, in addition, on mating component relative material strengths, nut geometry, and coefficient of friction between thread bearing surfaces. Effective shear areas are therefore somewhat less than the geometric values.

In general the length of engagement of mating threads is selected to utilize full tensile strength of a bolt prior to shearing of nut threads. Other applications may require internal thread shear prior to failure of the externally threaded part.