I have two Mikuni carbs and I'm having trouble identifying which carbs I have (since there are no markings on the body of the carb).

One was given to me and is supposed to be an HSR48. Thinking the HSR48 was going to be too big for my current project, I ordered an HSR45 (HSR42 would be borderline according to my builder).

When I received the HSR45 I started comparing it to the "HSR48" and they appear to be identical. The inside diameter of the inlet nozzles on both carbs at it's smallest point is 48mm. The inside diameter of the outlet nozzle on both carbs is 45mm.

Unless the new carb was inadvertently shipped in a box that was labeled incorrectly (original box marked HSR45), I'm assuming that both carbs are HSR45s.

All that being said, am I correct in assuming that you can determine what carb you have by measuring the inside diameter of the outlet nozzle?

TIA