Top tube is oversized isn't it? The normal lug set would be sized for a 1" top tube, that looks to be 1⅛". Similar treatment at the BB as the down and seat tubes are conical so the BB ends wouldn't fit in the sockets of a regular shell.
Correct. Serotta made his own BB cast, for the proprietary tubing he did with Columbus, in ‘91-‘92. Mine is from 1990.
@Thrust started
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Top tube is oversized isn't it? The normal lug set would be sized for a 1" top tube, that looks to be 1⅛". Similar treatment at the BB as the down and seat tubes are conical so the BB ends wouldn't fit in the sockets of a regular shell.