If you live in an area with risk of freezing pipes or water leakage, you should have a key like this on hand so you can turn off the main shutoff to your home. It is also good for monitoring water consumption while a sprinkler or appliance runs.
I printed mine with 5 perimeters and 50% infill. I'm not sure exactly how far I can scale it back, but it prints pretty quick and is sturdy and works. I included an Ender3 GCode file in it as well, if you wanted to jump over the slicing.
Accepts a 3/8" ratchet to turn the key. Pictured is a 3/8" extension, for clarity.
The author marked this model as their own original creation.