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snottyotter-
As best I can measure, about 27 with the tube walls at 1.4mm. That's odd isn't it? Though writing this makes me think @M_V 's point about external butting might be on the money - these numbers would add up then. If that's right, then I'd need a 30mm clamp and hope that works with a 27.2 post. Just a bit nervous as it's getting closed to the brazing.
adamdenw
I need a seatpost clamp for this frame - looks to be 30mm external but that would suggest a 28.6 seatpost, right? There's nothing that would be 30 external and 27.2 internal?
It's a Roberts frame (no tubing decals to give a clue there) with seattube cut down before I got it as original top had cracked where overtightened. So .. a bit chicken& egg as have neither the clamp nor right size seatpost, only 27.2mm one which didn't seem that loose so now I'm a bit confused... Thanks in advance for any clarity.