'72 rear wheel stud dilemma

[likaroc13]

so, i'm swapping a '72 1/2-ton truck rear into my '66 C-10...my dad went to get a new wheel stud today for one that's broken...every parts store shows the size to be 1/2-20...but the issue is the knurl diameter...Rock Auto says the knurl is .535", but the stud my dad took out is bigger...it measures .6xx

i don't see anywhere that there were 2 different size studs for the rear...anybody have an idea?

thanks