Originally Posted by
3alarmer
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...one of the things you realize after you've encountered enough of them is that seat posts are not always standardized at the diameter marked on them, and frames are not always reamed to the standards you expect. So if it's an alloy post, there's no reason not to carefully sand down the portion that goes into the seat tube a skosh to get .the fit you need.
I had to do that and it worked out well. It was a 27.2 post to replace a 27.2 post but the new one wouldn't slide in. I ended up sanding, carefully, for about two hours because I didn't want to take off too much. I started with medium-coarse emory cloth in a shoe-shine motion but really didn't make much progress and switched to a power sander. Just a little at a time, stopping and checking often, until it fit. Steel, not alloy.