There's other silly ones. Wood has been metric almost as long as I can remember, but 50x25mm is still commonly referred to as 2x1 etc. If it's PAR it'll be smal

There's other silly ones. Wood has been metric almost as long as I can remember, but 50x25mm is still commonly referred to as 2x1 etc. If it's PAR it'll be smaller than either. :) plumbing pipes and fittings are still mostly really BSP - British Standard Pipe uses inside diameter, metric outside. 15mm pipe and fitting is really a 1/2" BSP with imperial thread. UK was probably too lax about it to be honest. They didn't require all packaging to use metric only until the last 20 years, so plenty of shops kept on putting up signs in pounds even if the till worked the price in kilos. Since metric packaging was required there's been one clear downside - you're far, far more likely to have manufacturers hide price rises by dropping 5 or 10 ml or grams from a product, in an apparently identical pack. Repeat a few times and much is now randomly sized, where once all brands had comparable sizes. Choc bars, jam, used to be 1lb, 1/2, 1/4. Now some random number of g.