Seatpost sizes go to one more decimal place, and customarily are in mm.

Sizes could be 26.6, 26.8, 27.0, 27.2 or 27.4, and each infers that a certain type of tubing was used - which was why I inquired. I wish I still had my "Buyer's Guide". It has hundreds and hundreds of makers listed. Might help with the ID here.