I was out of M3 screws longer than 8mm, so I reworked mgx's very good belt clip to have one half used as a "plastic nut".
Although I tried to make the clip grip the belt even tighter by removing some material along the edge and offsetting the teeth on one half of the clip.
The two halves are no longer interchangeable, you have to print the pair. Assemble with an M3x8 screw.
Printed in PLA at 0.2mm. Works beautifully on my Kossel mini.