A23. 12x1 female side mount Ciao
Links to photos of examples:
1974 Vespa Ciao frame
This valve fits a Vespa (Piaggio) Ciao. It can also fit a Puch Maxi type frame, but the upper filter hits the inside upper wall of the Puch gas tank. The reserve tube, which is a light press fit, can simply be rotated so it is not aimed straight up, to allow a Ciao valve to fit a Puch.