Aircon refill on C4 A6

[MikeH]

I've bought a Halfrauds refill kit for the '96 A6 C4, but the standard port fitting in the kit doesn't fit the low side port on the air con condenser (radiator).

I'm having no luck finding an adaptor. Does anyone know what the spec of the connector is, or where I can find an adaptor to refill it from the standard kit.

I've already bought one ebay adaptor that looked like it might work but didn't, so I'd rather avoid spending more money without the right info.

I've also got a '97 C4 Quattro TDI, so I've got 2 cars to do, and would like to find a way of filling them myself. Both had a faint pressure hiss when I pushed the valve, so not completely leaky.