Originally Posted by
veganbikes
Take a set of dial/vernier/digital calipers and measure a few times around but it sounds like 26.8 is the right fit. I am surprised you haven't run into this issue before though, it is pretty common I usually measure a 3-6 seatposts a year at least and sometimes more. Not super often but frequent and common enough. Stein still makes their sizing rods at least of a couple years ago. I would suspect any level of shop would run into someone with a seatpost sizing issue but I guess if you only work on purely high end newer bikes maybe less of an issue?
I've run into the wrong size post damaging the frame many times, and have fixed them. The thing that is different here is that the damage is subtle and the next size down fits so well I can see not messing with things. So I'm trying to figure out what does more harm - a slightly wrong post, or re-bending the lug to get back the missing .2mm.