Measurements - Need some help

[puzzledpaul]

Last pic is correct solution - but not easy with wing's toolset.

I tried another 'eyeball' way which is easier and produced correct results - to 3 dec places (I got 2.0003 etc and 1.9992 etc)

Needs a pic (ideally) to describe, but mrs pp needs pc soon.

... but I'll try

Using your pics
select inside top face of LH column and inside bottom face of RH column > Face | Bridge
Place a 1 unit diameter cyl in the middle - as you have done.

Now, to adjust both diagonal lines - at the same time (important) - use Shift | Planar > (LMB)
Select the 2 edges - in the acute angle between the diagonals and the columns
Y for axis (or any vertical edge)
centre of cylinder for origin of operation

Drag until diagonal edge(s) just touch circle.

I used 360section circle to get it 'round'

pp