Joined: Aug 2013
Posts: 833
Likes: 10
From: San Francisco
Bikes: '68 Raleigh Suberbe, '92 (German) Centurion Equipe, '85 Schwinn Peloton, 1983ish Zunow Road Racer project, '69 Squanch Super Tourer, 1980 Bianchi Super Corsa, '82 Austro-Daimler Vent Noir, '89 Miyata 914 project, 1982ish Bianchi Rallye
My similar Miyata Two-Ten has them on both sides. And the right side one is not part of the derailleur. I'm stumped too. Best guess is they do the same thing as adjuster screws - - to have a quick setting for keeping rear wheel angle straight. In fact, I think they can even be adjusted a bit. But I was wrong once.