AS3990 Maximum Permissible Stresses in Snug Tight Bolts

[DALOB]

In AS3990 there is a factor in the Bearing Stress calc for Max Permissible Stress in Snug Tight Bolts of 2.1. See below.


I was wondering if anyone can explain where is factor came from and why it is being applied to this particular calc.

Thanks,

Jason