Theres no mention whether this is a steel Swift, aluminum Xootr Swift or what vintage the frame in question is so I don't know if these measurements by dial caliper are useful. So for whatever its worth:

Dahon Speed D7 stock seatpost: 1.334" (33.8836 millimeters)

Dahon Telescoping seatpost: 1.337" (33.9598 millimeters)

Xootr Swift stock seatpost: 1.3375" (33.9725 millimeters)

Xootr Swift stock seatpost:


Dahon telescoping seatpost:


Unfortunately the stock seatpost on my Dahon Speed has no markings besides minimum and maximum insertion lines.

I'm not an engineer so the ones here can decide whether a few thousands or ten-thousands of an inch would be critical to seatpost diameter. I've been using the Dahon telescoping post on my Swift now for 600+ miles and 80+ folds/unfolds with no ill effects.