Your last post caused me to look at another column that I have, and that one is 3/4" dia. x 16 tpi, which is UNF thread.
If you are buying a bearing for here be careful with the size.
The ring on the floor and the inner diameter can be different sizes.
The imperial self alingning bearing is difficult to find and can be expensive.
I have one that so far, I have been un able to remove from the column.
The Australian carriers used metric sizing and use a cheap and easy to get 6304? (check) bearing.
This leads me to mention that I have found on Canadian carriers, that there are bolts which are hybrids (I am talking original bolts)
Some are UNF threads, that fit the British spanners, and some are BSF that fit American sized spanners. I'd be interested to hear comments from others on this.