As title, as per T2, T3, T4, and T6 flanges are called what they are, and are set sizes, does anyone know if there is a name for the 3 bolt flanges you find on some other cars?

Ta

 

Lots of Jap makers just use whatever they fancy at the time, usually despoke for whatever they are building at the time..

They dont have any names, or garret style sizing system.

Although I can say pretty much all the Subaru 3 bolt flanges are the same, except the newer twin scroll stuff. Not sure about that.