Assuming it is Columbus tubing, a 26.8mm seat post would be indicative of Aelle, which had a 27.0mm nominal, inner diameter, seat tube. If the inner diameter of the seat tube is 26.8mm, then it would use a 26.6mm seat post, which would be indicative of Columbus Zeta. Another check would be to examine the fork's steering tube. Neither Aelle nor Zeta employed the patented Columbus steering tube and therefore would not have the Columbus dove logo stamped on the outside or the five helical ridges on the inside, at the bottom.