Originally Posted by unterhausen

Did vintage French builders use thinner gauge tubing than 8/.55/8? How would we know? There is the mythical Reynolds 531 1/.3/1 tubing, but the only way to tell if you have that is if the tubes look like a golf ball from all the dents.
I guess 753 had .3 center section, and supposedly there is an 531 SL version to match. I made one of those, it feels really lightweight. But I don't think it's .8/.3/.8 I should slap an ultrasound on it to see how thick it really is.

When I build with OS or 2OS tubing, I get the .7/.45/.7 tubes that columbus sells. Never had any trouble with it, but it's approximately the same stiffness as .8.6.8 standard dimension tubing. If there is some other property we're talking about other than stiffness, I will point you to Unterhausen's law of cognitive bias.