A21. 12x1 female spigot right medium shaft
Links to photos of examples:
Vespa Grande: The Vespa Grande has a vertical type valve, but it is mounted at an angle of about 60 degrees from vertical, or “2 o’clock”, as seen in the red frame photo. Although the spigot direction is wrong, this still works fine on a Vespa Grande. The gas has to go uphill a little at first, but the gas hose stays below the bottom of the gas tank (when routed under the throttle cable like shown below). So it will flow gasoline all the way to empty.
Tomos Targa: While the Tomos Targa valve works on a Vespa Si, the opposite is not true. The Tomos engine is too close, unless the cover is left off and the valve is rotated.