Britax 2 Pin Plug & Socket, B62A.
Generally the centre pin is used for active/positive. The flexible rubber boot can be trimmed to allow larger wire. These are the same plug as used on the Australian Plug for Chescold fridges.
We have been selling this product for several years now. We try to keep plenty on our shelves for quick delivery. If you order more than the 16 we have in stock, the delay is around 5 days to get more.