When I had my carb off the other week I got 1.81" at the bottem opening, which is 45.974mm. I don't know how people measure the throttle plate inside the carb though?
If the throat below the plate is straight then you can assume it's a 46mm plate. However, not all carbs are straight after the plate. Novi 46mm carbs, for one example, taper out to 48mm after the plate. They're still 46mm carbs despite effectively being hourglass shaped. Their 48mm carbs are straight from the plate down.
So, it depends on the carb.