Set Screw Coupling of Sleeves
First, obtain conical set screws. We recommend Alloy Steel Cone-Point Set Screws, 1/4"-28 thread, 3/8" in length. Use an appropriate drill and tap (the set screws will self tap, so this is an option).
These set screws will dig into the tubing wall
Just drill with the appropriate bit, and thread (the set screws can self thread). Plan for between 4 and 8 setscrews according to your needs.
Butyrate tubing is excellent for fabrication. As it is a cellulosic, it cuts, taps, and works like a piece of pine.
Insert the tubing into the sleeve and carefully tighten with an Allen wrench.
Be very careful not to strip the plastic thread.
That's it. It's easy.