I dont know, but read a lot about this and have the pieces already ..
Many working spindles have been made, by amateurs.
From memory, the hole needs to be about 1:1 - 1:2 in diameter-depth, and 2-3 x D of conduit.
Ie
conduit 1 mm. Hole 2-3 mm D, and 4-6 mm deep.
The hole acts like an air reservoir, and the pressure-cubed law makes it very stiff, as the air in the whole hole gets compressed.
Just like citroen suspensions.
With grooves, it was 2-3 mm wide groove, 4-5 mm deep.
2 grooves at each spindle end, in the approx 25 mm D sizes.
Seemed it does not much matter, on sizing.
Affects rigidity and efficiency, but wide variance seems to work, by several examples.
Did not need super small clearances .. just that smaller might be more efficient, as I understood it.
Ie air bearings work with both 0.1 mm and 0.002 mm clearances.