Tube Connector with Captured Nut

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: http://www.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.