Often the strangest stuff I find on a firearm while investigating is that simply I dunno what that part is. Sometimes, it is something lost to history, and not there now.
This video had some stuff on the Lee Enfield I did not know. Or, at least, I knew in principle but seeing a real gun on video is different from reading or a diagram
It's a commercial version of the long Lee rifle, mostly for back in the day when officers were gentlemen, so you didn't get issued stuff, but bought nice versions. So, not being issue: never updated. When you find one, it's a time machine. Neat.
I had an SMLE III* with the loop for the mag chain. Never knew what it was for until now.
I am also reminded how much it is important to document stuff. Multi-part interview with someone at FN on the MAG58 a few years back, and one question to them was what is this funny little notch on the side of the gas block.
Answer: We have no idea. Reason is lost to the mists of time. BUT, so many of these are sold, for so long, to so many orgs, who use it in so many ways, they dare not remove it, even though it would save them (and their purchasers) a couple bucks. What if it has some very specific need? Or, it has been incidentally used for indexing to a mount or something, then your army buys new guns and... they don't work with the old gear. They have enough ethics they don't want to do that to any of their customers, who really need these things to work.