This is a Vent Plug spanner designed specifically for Gong Wingfoil boards, where the vent plug is located at the bottom of the carry handle. But should be useable on any board with a standard vent plugs (16mm across flats)
Gong recommend vent plug removal during air travel and even when board is subjected to rapid temperature changes (eg left on sunny beach after being on the water).
This provides a cheap, light corrosion, free tool, that can be left on the beach or even carried in a pocket.

Designed in fusion360.
No overhang supports required, if printed vertically.
I printed in PETG with 0.8mm nozzle.
Some other printer settings:
Layer height 0.4mm
Wall thickness 3.2mm
Top/Bottom thickness 2mm
Infill 20% - probably not needed as the strength comes from the skins

I set the hex socket to 16.4mm across flats (vent plugs are 16mm nom). This may require a little adjustment, to get a nice fit, depending on printer and nozzle size - Should be easily achieved by adjusting scaling in slicer?