I am going to use a Reynolds 631 seat tube 31.75mm diameter double butted 0.8/0.5/0.8 The nominal internal diameter of the seat tube is 30.15mm

It will be quite a large frame so there will be plenty of thicker butted section at the top to support the seatpost.

Build will be silver brazed lugs.


I am trying to source a seatpost and am not sure what range of sizes I could use. None of the sizes seem common so the more choice the better.

Would a 30.0 mm post fit? I know they have to be slightly smaller than the seat tube hole but would this work. It would be handy for me as I already have an adjustable reamer that will reach about 30.1
What would be the maximum size? Could I ream out nearly all of the butting to fit a 30.6 seatpost? Would this compromise the strength? I am aware people use single butted seat tubes 0.5 thick which makes me think it is fine, but then I also read you should use an externally butted tube.
Would 30.2 or 30.4 be a better compromise.

Not keen on using shims!

Thanks

Mike