Here's some more relatively obscure information. The steel tubesets were straight gauge. The combination of a relatively low curing temperature and the internal reinforcement of the lug extension meant that the tubes did not require butting to compensate for the strength lost due to high brazing temperatures. For instance, the 1990 Technium Competition had custom Reynolds 531 main tubes that were a straight 0.6mm. No 0.8mm or 0.9mm butts!