Building materials are classic for this, just did an order for work. 4" 3.6m posts, 1kg of 4" nails, 3.6m x 3.5"x1.5" Rails. Metric has its advantages like a litre of water is 1Kg but sometimes a mix just works. Yeah got a load of 2.6m 2x2" in garage but that works lol have seen 4x2 and 2x2 written in metric before and was totally confused metal even more fun bought some 6m 1x1" 1.25mm thick box section. But surely that is what we should be about, using what works and what people understand rather than 1 rigid system purely for uniformity.