> As far as I know where older 531 is concerned, there is no such thing as
> a "double butted" seat tube. Seat tubes can be straight gauge or single
> butted and are only butted on the bottom. There are standard gauge and
> heavy gauge seat tubes. The heaver seat tube will take the smaller seat
> post. For the most part French (metric dimention) seat tubes run between
> 26.4 and 26.8. Most common is 26.4 and 26.6 from what I've seen. I've
> seen some frames that use as small as 26.0 seat post, like my 1940's
> Follis touring tandem stashed under the house awaiting restoration.
Out of curiosity I took a dial caliper to the Simplex seatpost on my 1966 PX-10. It's 26.0 (1.025"). So here's yet another data point for the PX-10 database.
email@example.com (John V. Everett)