Its the right size. 27.2, like the old seat post. Its on my 531 frame I've greased it up, went in so far then stopped because it was too tight and wouldnt go in further. I sanded down the inside to get rid of the paint from where, and tried again. Then tried so i got all the paint out from inside. Greased up and went in. Goes in so far but then it dont go in further. It looks like there is a lip in the tube where the post is going, about 1cm down the tube, maybe less. Not from me sanding it. Has the two bits that squeeze together been squeezes together too much and just need opening? Says on the other post 27.2 and the new post is 27.2. So any tips on getting a post into a tight hole?