This is my Nema23 bowden extruder cold end.
It' symmetric design, so the motor can mounted to the left and right sight.
It uses a 4mm OD tubing.
The driveing pully should have an outer diameter of 12mm.
For connection to the bowden tubing the hols are met to use a thread with nominal thread size of 1/8" BSPP.
I printed it in ABS and cut the thread with a thread cutters direct in the mount block.
The bearing is a 6x19x6mm DIN 625. I cut a M& thread dircet in the idler block. The screw is a DIN 7991 M6x16mm gift screw.
The spring holder is a M3 threaded rod.
For the motor mount I used DIN 933 hex screws, the head fits in the extruder mount and can attracted from the motor side.