How is mm size determined on carbs?

[Tri-ZNate]

I have always ben curious about this.

[Huffa]

You mean how do they arrive at what size to use on a specific model or where they measure from?

If it's the measurement it would be the inside diameter of the front of carb throat I think.

Larger diameter is better for top end, smaller for low end.

[MTS]

verner cliper measure on the intake side side of the carb-the smaller non flared side.

[Tri-ZNate]

yep its the size of the throat I was asking. Thanks.