Measuring Turning Tools

How come the actual size of my gouges never seems to match the dimensions listed in catalogs?

The folks at Oneway explain that British and North American manufacturers measure gouges differently, which has proven effective for sowing massive confusion here in the colonies. While American and Canadian makers measure the diameter of the tool, the Brits measure the distance across the inside of the flute. Thus what we might measure as a 3/4" gouge could be described by its Sheffield maker as a 1/2" gouge. And we'd both be right, even if neither of us knew what the other was talking about.