Originally Posted by ser_gio

I have a vintage Italian-made Bianchi mountain bike from 1992. The original seat post was too short and rusty. I replaced it with a 27.2mm diameter post. The post fit but it did require quite a bit effort, some light pounding and twisting. Now its is too tight and hard to remove (not that I need to remove nor adjust). Unfortunately, I did not check the diameter mark on the original post before I discard it. From the manufacturer's specs, I see that they used 26.8, 27.0 or 27.2 mm seat post for that bike. Should I buy a 27.0 mm seat post to replace the one that I already installed? Would 27.2 mm seat post fit if the original size was 27.0 mm? Would 27.0 mm slip now that I installed/forced 27.2 mm into it? Thank you for your feedback. I kept thinking about this since my install.