@glyph my hobby: making up stories about "imperial units".

Like, how the story you usually hear about the dimensions of a "2x4" are wrong. yes yes, fresh vs aged wood, but that only accounts for about 28% of the actual size difference.

See, it's actually about the difference between the wine gallon and the ale gallon.

The gallon is BOTH defined as a certain weight of its constitutent liquid; wine and ale have different densities due to different alcohol content, so their gallons are of different weights.

But the gallon is also defined as 3×7×11 inches (nobody knows why! Usually imperial units like to divide into 2s, 3s, and sometimes 5s. 7s and 11s are really uncommon!)

How is this possible? Because there are wine-inches and ale-inches.

Most US lumber is actually from Canada, and in Canada they use a system based on wine-inches, while the US uses the larger ale inch.