Just dropping in a note. This thread was really helpful. I have an odd 1970's Italian bike, and needed a higher seatpost because the original one is only 6'' high, and I need another 1-2". I took it to the local bike Bikeline shop, they measured it as 26.0 (they're much better qualified to measure & actually have the tool).

The links in the thread helped me find a selection of 26.0 seatposts and order on-line.

I am just passing this along because whenever you include links/feedback - it helps.
Thanks...