|Yep, it reads 27.0 mm on that Avenir 4130 steel seatpost.|
If you're here for the purpose of rebuilding an old Diamond Back road bike, you may be interested in learning more about my pepto-pink '91 Master TG, which I discovered nearly unused a few years ago. Good luck with your project!
|Seat cluster from the back...|
|...the left side...|
|...and the right.|