The pole goes inside adapter in contrary of original model. The hole size (and pole diameter) is 22.5 mm. Walls are 5mm

Here are 2 files: One as with original thread part unchanged from remix, it used for car mop. Another is 18.5mm which is standard for any US paint stick, mop, broom and so on.

Make it strong and solid. PLA or better, PETG. 0.2 mm height or higher will suffice, no need to make it thinner.