Print at highest quality possible. Parts are designed for strict tolerances. If your printer is not well aligned, you will get imperfect rotational bodies that will jam rotation. Clean parts carefully and break in rotating parts to make them run smoothly. You will have to cut or sand bumps and edges on the upper and lower flanges where the runner fits tightly in the housing.

My first attempt was printed at 0,1mm layer height and 25% infill. The shaft was printed with 100% infill. Housing, runner and cover plate need support structures, all other part printed nicely without support. Support structures "touching build plate" will suffice. The housing part is supported by the internal blades. Some imperfect ceilings because of too big bridging distances are not visible when assembled. The handle prints with the flange layed flat on the build plate. Add brim support to give additional adhesion.

The handle is designed for a standard european thread. I think there's only one, don't ask me for the exact size or specification. Just took the measures from the original shower head. Maybe I will add other sizes later, if requested.

No gaskets used yet. Parts are fitting tightly enough to let no water spray out. Some water dripping out does not bother me too much.

Use M3x10 and M3*16 machine screws. I also tried countersunk head wood screw M3x12 and it works very well. Drill the holes a little bit to get a proper cone fit.