I'd take it to a good bike shop & have them drop a seat tube sizer in there. Act like you might buy a seat post fom them & they should size it for free.
Dont really have time to get to a bike shop fella, and the nearest one that'll have the tools is miles away and deep in the depths of congestion city :roll:
I have put a tape measure across the opening and it measure's bang on 25mm, but obviously it may be 25. something..
Anyone else know... had a look on the net and came up with zip.. :roll:
Just had a 1" steerer in there to judge for size, that is 25mm I think, it fits in a treat but has a very slight bit of play, would it likely to be a 25.2 or 25.4 ?