Actually, there is quite a bit of imperial measure used in bikes. Pedals are 9/16-20 unless they are 1/2"-20 or french. 25.4mm handlebars are 1", seat posts are generally fractional inch sizes translated to mm, as are tubing sizes. One of the things that made french bikes weird was they were all metric.
Jeff, check your math. Down here we get 15.4 grains to the gram. I bet you meant milligrams.