Feeling rather stupid...
I'm looking at the picture (which is also figure 19 in the Outdoor Access Point Planning and Installation Guide)

and I can't figure out how this relates to the four pieces which came with my AP-377...
Does it go on the end that screws into the AP?
I've got the 2016 and 2021 versions of the document -- maybe some updated pictures are in order?
Also, I have 4 AP-377EX versions, and they come with yet a different cable glands assembly that's metal. Are there instructions on how to assemble that?