I've just acquired a 1959 175TS, but unfortunately it is missing a few bits and pieces including the rear wheel spacer. I've got a copy of the original parts manual and it appears to be a similar shape to the front speedo drive. 15mm wide with a recess inside for a felt washer to protect the rear wheel bearing one presumes?
I can get one made up locally, but would really like to make it authentic and profiled like the original. If anyone has some photos/more accurate dimensions that you could post or send me I'd really be grateful.