I have a Tubus Airy rear rack on my bike, and I have kind of been wishing I could mount a Specialized Stix taillight to it in a clean fashion. This adapter clips onto 10mm tubing, and then is held in place using two M4 screws with M4x4 heat-stake inserts; you can then screw a taillight to it, as needed. Because the Stix mount has a little thing sticking out of the back of it, this has a channel to clear that.
I recommend printing this out of PETG rather than PLA; PLA doesn't flex enough to happily clip over the tubing. I used Proto-Pasta Empire Strikes Black; installing it over the tubing requires a little bit of believing in yourself. Hardware required:
I printed with tree supports on my Bambu X1 Carbon. Tree supports suck on PETG but what you gonna do. At least the supported side is not cosmetic. Print with the side of it against the plate; you want the clip's flexible axis to be printed in the X-Y plane, because they're going to bend a bunch in order to fit over the tubing.
Modeled in Onshape; here's the CAD link.
The author marked this model as their own original creation.