Re-balling a ball nut - what size increment for new bearings

I have approx 0.1mm of back lash in my Y axis, and im pretty convinced it is in the ball nut. Final measurements still needed to confirm, but I know it isnt in the screws thrust bearings. Anyway, my question is, what size increment would I go up with the balls. I don't expect to get it right first time, but where do I start? Its a rolled 1605 screw.

I recently did this on my screws. Is this for a single or double ball nut? Double nuts are adjusted via the shim and not oversized balls. Single nuts you can oversize and I would go in increments of .0002"

The screw came with .125" gr25 52100 balls most likely. When measured with a mic they can read as much as .0004" depending on quality of the mic. Also it is possible to flat spot the ball of your not ginger with the mic.

A lot of this depends on if you have a reliable cheap source for the variable ball sizes. The .125" are usually plentiful but the local small quantity supplier here in the states, Ball Tec has a wide range of prices for all of the other none normal sizes. I would buy a set of .125 balls and rebuild the screw. After a bit of run in see how these feel compared to the original. If it's about the same go up .0004" if new stock size balls make a considerable difference then only go up .0002" increments.

What was the backlash when the screws were new?

Use a good indicator and pick up a lead on the screw. Place the base on the table if the nut is tied to it. You can see the backlash on the indicator. This will take out any error from the thrust bearings.

Thanks folks. The screw and nut are new. GTEN brand bought here in the UK from a UK supplier. Its a single nut, there's no room for a double nut on the y axis even if I could afford it. They weren't bought as a matched pair. I cant be sure it is play in the nut/screw causing it just yet.