My factory 1963 front bar is 13/16”. The Addco 199 bar that I replaced it with is 1 1/8”. I just measured both to confirm. I have not driven the ‘63 as it’s still being built. I was commenting on my 1966 Catalina that I put an Addco 857 bar that is also 1 1/8”. That made a big difference even without adding a rear bar although I’m sure that would be better.
I did see the 199 bar described as 7/8” in a few ads but unless they’ve changed it, that’s incorrect. Mine is 1 1/8” and fits very tight.
Hope that helps you!
Here’s a link…..
https://www.sfxperformance.com/parts/ADD199.htm