What do your calipers tell you about the ID of the seat tube? If it is 25mm as well, I'd believe them.
25.4 mm (one inch) has been a standard size for a long time, but French bikes were 'different' for a long time, too.
Edit: If Thomson makes their 'Elite' seatpost in your size, it's a good, light, two-bolt adjustable aluminum one.
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Beneath the valley of the underbikers.
Last edited by Fredo76; 02-26-24 at 01:32 PM.