I saw the listing for this rest and sorry to say I was just guessing. I don't have one on my Roadmaster. So I may be wrong. Hopefully someone may have a better answer. My apologies if gave an incorrect answer. Just thought it made since and of course Indian didn't have a photo to go with the part listing.
this seems to be a good a place as any for the passenger drink holder, you will need the passenger armrest kit though.
Since I don't have them you must be referring to the nut on the underside of where the arm rest pad is installed? I guess it could be for anything you can fit there with a bolt of the same thread dimensions. This post is really all I've seen. Didn't see any peer reviews or anything on YT with a simple search for the Indian passenger arm rests. Indian channel has a guy holding it and you see the nut, but doesn't say anything about it.