[CR]Headset question

Someone asked me to help them find a Clip-Style Headset for a '40 Bates they are restoring. I had never heard of one. I found a pic of one on a '39 Hetchins that Peter Naiman sent me a link to. http://www.hetchins.org/504anglo1.htm. Then Rod Kronenberg asked me what the function of the clip is. Again I haven't a clue. Perhaps some of our savants can explain about them. I don't seem to be the only member who isn't familiar with them. Sorry if this might have been a topic before I arrived on the scene.
Thanks,
Tom Sanders
Lansing, Mi