Comment by johnwalkr

Machinists have no problem working with designs in SI units on an inch-based machine. Lots of American companies use metric in designs and machine shops have to deal with it, although shops are moving to metric more and more. When they do this they keep and use their old machines with no problem although it’s an annoyance. Conversely metric machine shops can make inch-sized parts with no problems. Lots of material stock is inch-sized in the US, so even when you design in metric you have to consider this. But over time there is more metric stock available in the US, and for things like precision shafts there’s no cost difference anymore.

Regardless of everyday usage, in mechanical engineering/metalworking, the switch to metric has already been happening slowly since the 70s. Old machines and designs can stay in inches but most industries are already moving to metric unless there’s a compelling reason not to. You can see in Canada what things have stayed in inches because of regulations and material availability. House framing and steel weldments come to mind.