Originally Posted by Trakhak

Interesting. Thanks for mentioning 708. I can't remember whether I ever even heard of it before encountering mentions on Bike Forums, and I've been a fan of Reynolds bikes since I got my first 531 bike, a Helyett, in 1964.

Just did a search and found a blog post speculating on why 708 is so rare that even most bike enthusiasts don't know of its existence.

Quoting:

I can think of one other possible reason why, not only did so few people buy bikes made from 708, but why, apparently, so few (comparatively, anyway) bikes were made from it. A butted frame tube has the same thickness through the circumference of the tube. This means that whether the builder or manufacturer brazes or welds the frame tubes together, and whether or not lugs are used, a consistent level of heat can be maintained around the circumference. In contrast, ribbed frame tubes have thick and thin sections, which makes it more difficult to maintain consistent heat levels. An area that is heated more loses more strength than one that is heated less. Thus, I imagine that it would be more difficult to make a strong joint with ribbed than with butted tubes.