UNC Fasteners in Tension
 UNC thread :
ISO 724 SAE Grade Number :
 Preload as perc. of proof strength :
 Major diameter d in mm
 Threads per inch N -
 Pitch P = 1/N in
 Pitch diameter dp = d - 0.649519/N in
 Minor diameter dr = d - 1.299038/N in
 Tensile stress area At = π/4 ((dp+dr)/2)2 10-3 in2
 Proof strength Sp kpsi MPa
 Initial preload Fi lb kN
1) Definition of proof load (externally threaded fastener): The tension applied load that a fastener must withstand without any indication of permanent deformation or failure. Proof load is typically calculated at 90-93% of the minimum yield strength.
2) The yield strength of SAE 5.2 and ISO 8.8 are approximately the same.