Colnago seat post advice

[Colnagoni]

Hi
I'd be grateful for any advice on seat post sizing for my Collage Super - I bought the frame a couple of years ago (when I was just starting out in this wonderful world of vintage bikes). However just before Christmas the seat post bolt failed on a ride and, having read around the subject a bit more since I first acquired the frame, I had come to realise most Colnago's of this period are 27,2mm whereas mine has a 27,0mm seat post currently fitted.

So I was wondering if anyone had any advice please - do I replace the seat post bolt and carry on, or should I be thinking about engaging some expert help to get a 27,2mm post in? I can't see any markings on the bottom of the seat tube to indicate what the correct size is. I've included a photo of the top of the seat tube which, in my limited knowledge, doesn't seem to show the bolts been overly-tightened in the past? I've tried fitting a 27,2mm post but it won't go into the seat post more than 4 or 5mm before needing extreme force to get it any further... ?
Many Thanks

 

[keithglos]

Re:

Is it possible Colnago used a thicker seat tube because of the frame size?

Keith

 

[Colnagoni]

Re:

Hi
I'm certainly hoping so - I think bikes around this time did come in more than one tube size and hopefully someone with a bit more knowledge than me can confirm this
Cheers