For whatever reason I had to make another 37D Motor Mount (I guess I like these motors)
In the middle of building it, I had mounts for one side and realized that some applications may need only that. So I went ahead and provided "one sided mount" versions as well.
The slots are intended for M4 or #8 screws. (If you need a bigger screw than that your design may have bigger problems!)
For my purpose I needed a model of the motor as well, so I included that. (Most motor manufacturers have models you can download, though the formats might be odd - nowadays there are online format converters available though).
Full disclosure: Gearbest gave me the CR-10 that I printed this with, so I feel sort of obligated to put it through it's paces.
You can increase the shells/infill for "stronger" motor mounts.
You might get away without supports, but the top of the mount might sag a bit