This is a hook that clips on the front of wire shelving in the Rubbermaid Fastback line.  These shelves have some variability in the wire-to-wire spacing, so some adjustment of the relevant model dimension may be required to achieve a tight fit to the shelf.

I recommend printing on the side with the hook parallel to the print surface as shown ih the cover photo.  I printed with support material under the hook.  This avoids having possible layer shear in the direction of weight supported by the hook.

I printed in Prusament PETG with PrusaSlicer default settings and cubic infill.