Print with 30% infill, 0.1 layer height, 4 walls and 8 top layers.

Sand mating surfaces of the middle part with 80 and then 200 grit.

The top and bottom parts should print smooth enough to make sanding unnecessary. They should be able to slide around freely in the middle part.

The coupler goes between your Z bracket and the brass nut, as shown in the photos.

INSTALLATION:

1. Make sure your parts are able to slide in eachother freely.
2. Support your X Axis with something (a box or similar) so it doesn't drop down while installing
3. Unscrew the upper bolt of your motor-screw coupler and remove your Z screw by winding it by hand, moving it through the brass nut
4. Unscrew the brass nut and fasten the upper coupler part in its place with 2 screws and 2 nuts
5. Attach the brass nut to the bottom coupler part as shown in the picture with 2 screws
6. Slide the bottom and middle part together and slide the middle part into the top part which you mounted before and put in the Z screw again, screw it in until it reaches into the motor coupling again.
7. Tighten the motor coupling bolt and you're good to go!

This coupler enables you to compensate for bent or cheap quality Z screws, it allows your Z screw to move around without affecting the X axis with horizontal movement.

It decouples both axes to only transfer Z movement.