obviously, a double-butted tubeset will be thinner all around than a single butted tubeset, otherwise the single butted set will weigh less. therefore, the single-butted tube is likely to be thicker both unbutted, and after butting. it was my assertion that maybe the thin "butted" part of a single butted tube was as thick as the thick "unbutted" part of a double butted tube.
i really should stick to stuff i know (e.g. not framebuilding).
i hope some 531 framebuilder can clear this up for us.
- Don Gillies
San Diego, CA