Thank you 3baygarage. I'll try to post a couple more pics of a side by side comparison of my new WF-21-S and my Bell System equipped WF-21 example. While they are similar, all the Bell System examples I've seen have this smaller aluminum knob rather than the larger wooden knob on the 21-S. The 21-S probably did serve some similar purpose and hope to find out what that might have been! Thanks again for the feedback.