That is a very curagouos statement. Tern seatposts have typically 33,9mm diameter and while this is common with Tern and Dahon bikes it is definitively not what "most folders" are using. There will no doubt be some using 33,9 as well but more where such a post won't fit. Checking the diameter of the existing post before going on the hunt for a longer one is the only valid option.