Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4856091. This is a spring mounting clip for 35mm DIN rails. It includes mounting holes on 35mm and 40mm centres, which have an internal diameter of 2.5mm (which can be tapped to accept M3 screws, or you can screw them in directly). I've added a second version which has slightly larger 3mm holes also.