Bloody Google, I'm non the wiser now! One says my suggestion, t'other says its a tinware bung, t'other says its a Porsche bung
Ha - schoolboy error Mark, you've got to look past the first three hits! apparently. allegedly. probably. Not me though, I just know stuff.
It is and I want one. If someone were to 3D print one that didn't mind getting a bit warm they'd sell 50 just on here straight off judging from the dipstick boot thread.