If you don't know what it is, why do you need more?
What's it going on? What did it come off of?

Good questions. Do you know what it is?

Here's where I found and it and why I need more.

We have some installed landscape lights that came with the property. Here's a link to them.

http://www.kimlighting.com/products/louvered_body

They come with a 1/2" x 12" stem to mount them on. The original installer must have thought the 1/2" stem looked too small around for the size of the light and decided instead to use 2" rigid electrical conduit. They do look much better with the larger stem. The point of attachment on the fixture itself is 1/2" female pipe thread.

To attach the 1/2" female fitting to the 2" stem, the following parts were used: (1) 1/2" short nipple, (2) 1"x1/2" rigid conduit bushing, (3) 1" union, (4) 2" union and (5) the part pictured above. See attached picture.

We're installing some new lights and want them to look the same. I can easily find the first 4 components. It's the 5th one I can't locate. I don't even know what it is to be able to do some google searches. It really looks like a rigid conduit bushing except that the inside is not threaded and it has the 2 notches, presumably to tighten and loosen it.

That's the story and I'm still trying to figure out what it is and where to get them.

maybe the threads were drilled out

Looks a bit like a plug used in a sealing fitting for Chapter 5 Articles. Likely is very old. Originally solid with no center hole. The user could have drilled out the center.

Thanks for everyone's feedback. We came up with a different way to achieve the same goal with fewer parts.

Thanks to fellow forum members joefixit2 and bus_driver about drilling out the center of a rigid bushing as that turned out to be what the original electrician did when he installed these. Question answered.