throttle body sizing

[Bartman420]

i have seen different sizes of throttle bodies for fuel injected models. where are they measuring when they talk about 50mm, 58mm and so on? at the air cleaner or at the head? i figure it's the inside diameter at one of those two places.

 

[hogrotten]

They measure at the largest part of the manifold wich is the air inlet behind the air cleaner.