I keep thinking I’ve seen the peanut shaped end holding a snare set… basically the chains bunch together … As a snare addition is so cheap you wouldn’t find them as parts, so unlikely anyone photographed the rod on its own…
Does the rod attach to the side of the drum and put that peanut up at the drum skin surface ?
Does your friends spouse/mother/other have a sewing machine? Because it looks like the guide arm (called a channel spacing bar) for ensuring your channel stitching is evenly spaced. The one I have has a flattened end like that.
You might be on to something. The rod shown at #4 resembles the OP’s mystery piece of metal. (I know next to nothing about sewing, so this is just based on an image search and your piece of info.)
Here’s an image of a complete set of triple sole walking feet. It looks like that particular part is called a seam guide. I’m not sure if that’s what exactly it is, but it looks pretty darned close. Maybe some quilters/sewers can help us?
ETA: Whoops, in my detective search, I neglected to notice that TheFaerie has named the part (I assume “guide arm” is the same thing. Yes, my brain somehow just glided over that second sentence while I was search for “sewing machine parts” or something like that.) No attempt to take credit away from where it is due. So a sewer has already chimed in. All credit goes to TheFaerie (but hopefully the additional pictures help). Sorry. 
I think you may have figured it out. It sure does look similar to the images pulykamell linked to.
No worrries! I couldn’t get my links to post correctly, so you were very helpful.