I keep using this example: In the wood shop, I’m going to cut a bridle joint. Requires cutting boards into thirds of their thickness. Metric lumber is often milled to 19mm thick. What’s a third of 19mm? You want to show me which line means 6.3333mm on a metric tape measure? US Customary lumber is milled to 3/4" thick. What’s a third of 3/4"? You want to show me which line means 1/4" on an inch tape measure? Now let’s cut a half-lap joint in that same lumber. In metric that works out to 9.5mm, there’s also no line on a typical metric tape measure for that. But there is a line for 3/8".

I’d much rather build furniture in inches than millimeters because in the wood shop I have to divide or multiply by powers of 2, 3 and 4 way more often than powers of 10. It is in this context that the inch standard which is subdivided by powers of two rather than ten arose, and it still works very well.

Metric users often correctly accuse Imperial or US Customary (though the two share names of units they are not identical) users of making excuses or relying on workarounds, in the context of woodworking joinery I find it’s the reverse. “Of course we don’t use 6.3333mm, you just know to cut the cheeks 6mm and the tongue 7mm. 6+6+7 is 19.”

I’ll grant you, doing stoichiometry in ounces and pounds would be a fucking nightmare. But woodworking joinery? Nah I’m doing that in fractional inches.