Well yes they do when materials are sold in terms of "gauges" and I'm in the hardware shop (away from references) and faced with packages marked only in those terms.
As a scratch-builder I need to make a lot of conversions, sometimes, as in the example I've given, in situations where I don't have conversion tables or calculators handy.
Aircraft navigation has always been in imperial measurements. As I think I've already stated that most of my prototype data is imperial, original plans etc not having updated themselves during our conversion to metric thirty years ago. But I'm prepared to live with that. The problems are with dimensions of materials available to me and in particular having at least five different measuring systems involved.