Fatbars are 1&1/8" (I think) at the clamps, tapering to 7/8" (22.2mm) at the handlebars themselves.
7/8" has been the standard for a long time, with the exception of some middle age poser bikes which run 1". No doubt there's some oversized, over-blinged junk available in 1" if that helps?!
I don't understand what you're trying to achieve.