The funnel on my moka pot has a "crimp" -- a little ring-shaped indentation -- around the middle, similar to this one from Bialetti:
What is the purpose of this crimp?
It is indented toward the middle of the funnel (i.e., not protruding out of the funnel). It's far too low to indicate recommended "fill line" for quantity of grounds (for my taste anyway!) There's no other attachment that fits into it, nor does it engage with any other part on the pot (e.g., the top lip of the funnel sits on the moka pot base). It's one piece of sheet metal; e.g., this isn't a point where two pieces attach. Some moka pots have funnels that have this crimp, and others are solid/flat around the side.