We shall burn down ye haystack in the night, ye non-believer. 
Seriously however, in this instance, 12mm is so close to 15/32 as to be barely noticeable.
0.4724" - 0.4686" = 0.0037" (about 4/100ths of an inch or 1/10th of a millimeter)
I prefer the traditional method, the water cooled grindstone outside the blacksmiths shop hand turned by the village idiot. 