During a remodel, we lost the plastic key that opens and closes the circa-1971 ceiling heating vent in the master bathroom. This Thing is a functional replacement for that lost key.
It's designed to replace the key for the Hart and Cooley Butterfly Damper: http://www.hartandcooley.com/products/12/butterfly-damper-for-16-diffuser
The photos show the vent cover the key works in, and show the replacement key compared with an original.
To contrast the drab, 1970s vent cover, replace your existing keys with brightly-colored ones!
(I used an original Lulzbot Mini; the page doesn't offer "Mini 1" as an option.)
I printed in PLA, because I like that PLA will eventually biodegrade.
Print the parts as oriented in the STL files: print the long part with the flattened edge down; print the smaller part with the pins up.
If the pins don't fit in the holes, widen the holes a little with a drill bit or hobby knife.
Glue the small tab into the larger rod part, aligning the tab's pins with the rod-part's holes. I like to use E6000 Craft glue because it tolerates small gaps better than superglue.
"HeaterVentOpenRod v4.f3d" is the Fusion 360 design file. Walk through the model's timeline to get a feel for how I put this model together.
I measured the original part (from another vent in the house), and used those measurements in Fusion 360.
One difference from the original: I rotated the flat part of the rod, and split the curved tab in two so that I could print the rod part on that flat face, with no support. I added pins in the tab and corresponding holes (with 0.5 mm clearance) in the rod-part.
The faces that meet the print bed are chamfered 0.5 mm to compensate for first layer overextrusion ("elephant foot").
Because the curved tab's only function is to give you a handle to turn, you could redesign that tab to be more decorative. For example, you could make it look like a toy wind-up key, or an elephant.