Actually there are some. We used to have a lot of trouble with this, I don't remember the numbers, but you take something like a 1/2/ 5/8 etc saw arbor, will likely have a metric OD bearing with a standard metric number BUT THE BORE HAS BEEN HONED to fractional. The modified number is then "inked" onto the outer race WHERE IT WILL WEAR OFF
So people would come in, buy a bearing by the number stamped on the shields, and then ruin it or the shaft trying to drive it onto the U.S. shaft
