TB b16 vs b18a...is there a difference?

Was wondering if there was a difference between the b16a and b18a throttle body…I mean the size/bore. I think my IACV is bad and the b18a TB can’t be unscrewed (its not held on by screws) so i was thinking about swapping the throttle body all together. Why, you ask? Cause a freaking new IACV from the dealer is like $200+.

TIA
Ken