I have a 5" 6 jaw chuck that is my go to chuck on the mini lathe. It cannot grip anything smaller than about a half inch diameter. So I end up switching it out for the original 3-jaw that came with the lathe. I bought a cast iron adapter plate from Little Machine Shop. It had a 1" x 10 tpi thread so I turned a piece of 1018 steel to .995" and single point threaded it on the lathe. Now the mini lathe chart only goes down to 12 tpi but LMS has a neat program that will compute the gear train to make any pitch from 1 to 256 tpi. It came up with 80 on A and 50 on D. Checked that with a scratch thread and it was right on. Then I simply faced the adapter on the lathe. Made up 3 screw points for the 6mm x 1 chuck thread and transfered the holes to the adapter plate.
I checked it several times and I can get it set to within .002" of runout. If I need better I will just have to change out to my 5C collet chuck.