Are you guys calibrating your micrometers against a known accurate standard at 68 degrees F on the day of measurement? Many smileys to show that I am JUST KIDDING!!!

But seriously, I don't know if there actually are any published tolerances on seatpost clearance (I know... I'm a whole lotta help!) But I would be willing to postulate that the intended clearance should be less than 0.1 mm. I am basing this on the availability of seatposts rated at 26.0, 26.2. 26.8, 27.0, 27.2, etc.

I would also say that 0.1 mm or less is definately a ballpark because a seat tube is finished off by a person handholding an electric drill driving a 3 bladed reamer, followed by a flex hone... So, it depends upon his mood and the relative tension of his anus...

(A hand-lapped seatpost? Geez, THAT would be anal!)

Although, I have read (on www.roadbikereview.com) that Moots waranteed a chronically slipping post because it measured "On the small side" of their tolerances...

Check with the bicycle manufacturer to be sure of the intended seat tube size if you're unsure.

And then don't get all dyslexic when ordering that 26.8 post for your 28.6 bike!

-Erik