UNC Fasteners
in Tension 

UNC thread : 

SAE Grade Number : 

Preload as perc. of proof
strength : 



SIunits 
Major diameter d 
in 
mm 
Threads per inch N 
 
Pitch P = 1/N 
in 
Pitch diameter d_{p}
= d  0.649519/N 
in 
Minor diameter d_{r}
= d  1.299038/N 
in 
Tensile stress area A_{t }
= π/4 ((d_{p}+d_{r})/2)^{2} 
10^{3}
in^{2} 
Proof strength S_{p} 
kpsi 
MPa 
Initial preload F_{i} 
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 9093% of the
minimum yield strength.
^{2) }The yield strength of SAE 5.2 and ISO 8.8 are
approximately the same. 

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