Off Set ver. Disc Caliper

[ck5566]

Probably been asked & answered but one more time. I here 3 nub rims 6 lug, 3.5" center hole is No good for Disc Brakes but the 4 nub rims 6 lug, 3.5" center hole is OK for Disc Brakes in that the amount of the "Off Set" has something to do with them fitting better or does the "Back Space" also have something to do with it. Whats the skinny about the fitment and how does the "Off Set" and or "Back Spacing" come in to the fitment. I will add a pic for the understanding of it.

Thanks in advance.