What's so hard about fractional sizes? if you want to know what is near to say 27/64" merely add 1 to the 27 then divide both numbers by the largest hole number possible or simply divide by 2 then try again you will come up with 14/32 or 7/16" as the next larger size to find the size smaller just substract 1
While I agree with the way Rick has numbered his wrenches all by 16ths above them if I were under a truck and sent the driver to fetch me a
#9 as in needing a 9/16" he might bring me a 9/32" because that would be the only wrench with the
#9 stamped on it or he might reach for the metrics on the other set of nails