Bicycle Mechanics - 26.7 seatpost?

Should I attribute a caliper reading of 26.7 mm on my wife's bike's seatpost to my own error, or is that the diameter of a post that goes into a 26.8 mm seat tube? Or is this possibly a really oddball size on a late 80s Schwinn Worldsport? I tried a few times to get the seatpost reading to come back 26.8, but I couldn't. If I want to replace that post, should I get a 26.8? Thanks in advance...

Seatposts come in both 26.6 and 26.8 mm sizes. The seatpost size database at Sheldon Brown's website lists the 80's World Sport as taking a 25.8 mm post. Are you sure you didn't read 25.7 as 26.7 by accident? The safest thing to do is go to the LBS with all three possibilities (25.8, 26.6, 26.8) and check with them. They might have one of each size lying around to give it a shot with. I wouldn't feel terribly confident in ordering a seatpost at the moment.

Thanks! I checked Sheldon's database, so I checked, rechecked, zeroed the calipers, rezeroed them, am confident it's not 25.8. Until I find out I was doing all that checking and zeroing wrong, of course, but meantime I will try out 26.6 and 26.8. Thanks again...

One LBS owner of 40 years or so says there are 40 different seapost sizes. Not an oddball at all. 1997 Jamis Eclipse = 26.8 seatpost. 1984 Centurion Elite 12 = 27.0 seatpost 1989 Schwinn Prelude = 28.6 seatpost. Have them all. If your LBS has one there is a seapost sizing device you put down the seattube and get the reading off the thing. Old school tool.

It turns out to be 26.6!! If we knew what year it was, I might submit it to Sheldon Brown's database. It was bought in 87 or 88, but don't know how long it might have been on the shop floor.

ps-> I never could get a firm OD of 26.6 from the previous seatpost, but my calipers locked right out on 26.6 ID for the seat tube, no error there at all.