Originally Posted by
Mackers
Measured a couple I have laying about .....
FWIW - here's how standards and tolerances work for things like seatposts
Posts are the nominal or a bit under, while the tubes they fit are the nominal or a bit over.
Think of the nominal size as the double yellow down the middle of the road, and the tolerance as the width of the lanes.
As a practical matter manufacturers set their targets off the nominal for the same reason drivers don't crowd the double yellow.
Following this logic, seat tube reamers are made 0.05mm over the nominal, which is the max. limit, because over time the reamers will wear and cut undersize.