Originally Posted by
Steve_sr
The specs on my frame drawing say 31.6mm. I don't think that there is a standard 31.8 seat post. I think a lot of folks get confused as 31.8mm is standard clamp size for handlebars.
No, there's no confusion between seat post and handlebar clamp size here.
Seat posts are still being made in the 31.8mm size. Here's an
example by Kalloy.
So yes: 31.8mm is an uncommon but "standard" (or if you prefer, "still in production and available for purchase") seatpost size.