Sorry for the late reply, I didn't see your post until now.
I don't have any of that rod handy so I can't tell you what size it was, but I can tell you that the capstans were machined to the correct scale size. A look at TTSM volume 1 would give you the figures. As to why yours didn't come out quite to your liking, it may be how you cut them. The drums weren't a continuous concave curve from top to bottom, the central part of the drums were flat. Also the tops were slightly convex and slightly narrower in diameter than the bases, which also had a wide edge as opposed to the fine taper of the tops.
Keep at it. When I made things like that I ended up keeping one for every 5 or 6 I rejected.