Torq Thust 15" to 18"?

[Reiner]

Hi Lex,

thanks for your reply and your example. :-)
I have a 68 swb fleetside c10.
My father bought him in 1988, the truck was lowered only with shorted coils in that time, but have 5 lugs and Disc Brakes front.

So i dont know what rear end year is has. It´s a 12 Bolt, and i think its the small one from 68, only with 5 lug conversation, because i have 10x15 with 4" backspace rear. And it fits very good.
How can i measure, or identify my rear end to check what year it is?

Thanks Reiner :-)