Yes, there is a threaded insert. The insert of lobed.

* Insert the smaller rod (with the insert) into the bigger rod.
* Turn the small rod clockwise to tighten so that the small rod will not longer side in or out of the bigger rod.
* Turn the small rod counter-clockwise to loosen.
* After you understand, insert the rod into the closet, expand to desired length, and tighten.

Note: Do not over tighten or it will be very difficult to loosen and/or you may break/reshape the insert or the larger pipe. This is not a connection which slowly tightens. You will discover that the tight/loose difference is only about 1/4 turn.