I've been using a variation of this case on the MK3 but it is for a PiCam2. When I upgraded to PiCam3's I realized the case this is based on (https://www.thingiverse.com/thing:2956323) does not work, so I remodeled it.
Requires an M3x16mm (or longer) screw and nut.
The author remixed this model.
Remodeled for PiCam Module 3