Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4808258.

This is a versatile cable tie base which can be used to mount small boxes, appliances, power supplies etc to a flat surface. It has raised edges to support the box, for example if mounting them on a vertical surface. Two of these bases are normally sufficient to mount small devices. There are two STL files which are "left handed" and "right handed" halves.

An easy way to position these is to put some double-sided tape on the rear to get the initial position right, then insert a couple of screws to secure them. The slot will accept cable ties up to 5mm wide.

By design this part has some bridging (5mm) but it prints very easily without supports, and is a quick print.