Seatback bag / cargo hook clip-on body

So my friend bought a VW Caddy as the kids are growing. It has 14mm headrest rods, but the front seat headrests are not removable. A quick remix of Part A added a 13mm 'throat' that allows it to be clipped on.

Unlike the original, I'd advise against using PLA as to clip in place securely, the gap had to be fractionally smaller than the rod, requiring a little give in the material - I used PETG. Your mileage may vary...