This is just a copy of some of my comments from the Thingiverse page that I thought might be useful:
It is called 1" EMT conduit but it is actually .93" outside diameter. I used Home Depot but Lowes should be the same thing.
3/4"-see comments below
These are zinc coated steel and are very stiff. The bearings work a bit roughly at first, then the zinc coating rubs off under the bearing after a while making a nice smooth surface. I just ran some hand edited G code that moved the axes back and forth until the zinc wore down. Then I sanded them just a bit with very fine sandpaper to get the sharp edges off of the zinc “race”.
I used a regular pipe cutter with many rotations of the cutter for a cleaner cut than with a hack saw.