'87 Schwinn Super Sport question
 

The 1987 Schwinn catalog states the Super Sport's main tubes is made of Columbus Tenax double butted chrome-moly. However the seat post specified is 26.6 mm. Shouldn't the seat post diameter be 27.2mm if it is double butted?

Not withTenax, which is a seamed tubing.
Seatposts on all the Tenax bikes I've ever owned were 26.6.
That's a nice riding frame, regardless.

"Double-butted" doesn't tell you anything about seat post size because it doesn't tell you anything about tube wall thickness - just that it is thicker at the ends. One butted tubeset could be 1.0/0.9/1.0 while another could be 0.8/0.6/0.8. Obviously the inner diameter of the tubes will be different despite both being double-butted.