Peter Jourdain asked a few days ago about seat post size for a Ideor Asso with Columbus Tubing.
Finally got an answer from my brother who has one, his is a 1958 53cm (ctc) example, which may make a difference.
His is 26.8mm!
Perhaps lighter gauge tubing in the smaller sizes?
The Campagnolo headset and seat post are original to the bike, all else was updated over 30 years ago.
John Jorgensen Palos Verdes Ca
Where I advised him the headset is the majority of value of his bike.