Originally Posted by fietsbob

"Thin" has a number what do you have in mind? pretty "normal" Butt say 0.9 centers of 0.7?

in a 9/8"/28.6,, OD seat tube that thinner number on the top, leaves your 27.2 seat post fit.

26.8-(0.7x2)1.4=27.2..

if you want to be fussy Take it up with the Pro who will be building your frame Just for you alone .

and expect to pay them what they ask.