I have the need to mate a 1/4" thick piece of aluminum to a 1/2" round tubing. I need to be able to slide the mated aluminum along the tubing, and be able to lock it in place.
This thing is the tube connector, with a captured nut on the side.
Although somewhat related to this thing: thingiverse.com/thing:8356
It is not a strict derivative, but rather in the same family.
You can easily create a mashup of this thing and some other things, and get things sliding along tubes.
The fillet is on the bottom to help with reducing the amount of support material needed. It may not help at all depending on your printer. You can turn off the fillet, and simply get support under the overhang.
It is fully parameterized, so you can specify the size of the tubing, the length of the connector, and the size of the nut to be captured, as well as the number of facets that nut has (default 6).