Mystery Part for 2006 Baja 25k

[vaskohop]

On the roof of my Baja, there is a front and rear railing that holds the light fixtures. The horizontal rail sits on a cupped plastic piece that fits inside the vertical rail support. The screw on top seems to tighten the piece expanding it in the tube and locking it in.
Anyone have a clue what this piece is called or where I could get it.
Other option I was thinking is locating a "T" connector?

[Plowtoy]

The first thing I thought of is a rubber expansion nut. Should be able to find one at any decent hardware store. The only problem with that is when they compress, they are designed to have a lip or something to catch on. I don't know how it would stay just by putting outward force on the aluminum pipe as shown.

[vaskohop]

Jayco Service has now helped me 3 times to find obscure parts and get them to my local dealer. Just for information, these are labeled:
Saddle, Dbl Star Assembly w/bolt #0196202

They were pricey at $20, but it beat trying to fabricate

[snipe22]

Looks to me that an automotive freeze out plug would do the job. Same concept. The more that you tighten the freeze out plug, the more it expands inside the engine.