IBM Series 500 1/2" tape reels--What does the little red peg do?

[Chuck Guzis]

I'm working with a batch of tapes that includes several IBM Series 500 7
track reels.  If you look at the back of the reel, there's no customary
thumb recess for removing the write ring.  Rather, the reels have a
small red plastic peg that extends through to the front of the reel.

Is this for ejecting the write ring (I haven't tried)?

In any case it's a bit annoying because it grazes the edge of the ring
sensing finger, making a little "click" every time the reel makes a
complete revolution.

--Chuck