[kd5bjo]

In an odd way, the US is fully metricized: they’re one of the original signatories of the Treaty of the Metre, and redefined all of their legacy units in terms of SI ones [1]. SI units are used directly in the sciences and most products have the SI equivalent listed alongside the traditional measure. I understand that industries with international supply chains, like the auto industry, are also mostly metric these days.

There just hasn’t been much of a reason for the purely-domestic parts of the market to switch: house builders are looking for 2x4 lumber, and won’t buy from a lumberyard that calls it 50x100mm. Knowing that, the sawmills continue producing the 1.5x3.5 inch profile that’s called “2x4” and anything else is a specialty item. Who has an incentive to push through the change?

[1] https://en.m.wikipedia.org/wiki/Mendenhall_Order