A16. 12x1 female spigot back with clear trap
Links to photos of examples:
This valve has a clear sediment trap. Anything heavier than gasoline, like water, dirt, rust settles at the bottom. The trap not only filters, but allows visual monitoring of the fuel for purity.
Whizzer The 2002 Whizzer tank takes a 12×1 thread gas valve. But the original Whizzer valve has no reserve tube or fuel filter. To have those, the 6.3mm hole can be drilled to 7.0mm. Here it is shown with a A16 “spigot back” type valve, but a A18 “spigot right” type would be better.