Don't print this thing by itself! This is a boolean punch, a modular functionality. It creates a negative space which adds a function to another object. In this case it makes a keyhole hanger in your object so It may be hung on a wall with no fasteners showing

Use Blender or a similar program to boolean this shape out of another object. This size is approximately the right size to use a standard drywall screw.

More details on my blog:

http://www.the3dprintedfuture.com