This is a holder for a marine-type key used for switching on and off an inverter. It fits under the switch housing cover and allows it to close properly.
I found that the original key is actually a bit elliptical in shape, so turning it a bit to the left or right releases it, while placing it in parallel with the cover it is a tight fit. Works well!
Mounted under the cover with double-sided foam tape.
Devil Design PETG
Print on its side, no supports needed.