Anyone know the diameter of that tube?

[mhorowit]

I'd like to build a hardwood collar to clamp onto the trailing edge of the horizontal staballizer.
Anyone know the OD of that tube?
I'd rather beat and twist on the collar than continue with the 'U" bolt/lever arm; anytime I use a flat surface against a tube I tend to warp it. This way I can take the pipe wrench to the collar! - Mike