UPDATE: There is an updated version of this hook which is 16mm thick and uses less infill. It is still exceptionally rigid and fit for purpose, but prints in half the time and uses half the filament. :) The thickness is selectable in the print profiles. The narrower version can use a single strip of 15mm 3m tape.

I made this simple hook to attach to the underside of my desk to hold my headphones.

I attached it to the bottom of my desk using 2 strips of narrow 3m tape. (This stuff).

holds very secure and cannot be pulled off easily. You could use a single wider strip but this is what I had to hand!