invercones are used with Weston meters, and as far as I know, weren't available for other meters. If you need an incident dome, that's something different.
Ah yes. "Invercone" makes much more sense, since only on the Weston meter does the dome have a big concave dimple, from which I would assume it gets the "inver" part of it's name, because it is like an inverted dome.