Working diameter is meant to be the size of the circular nut or object being turned by the wrench, as opposed to "pin" diameter. If you're speaking of clearance or tolerance between the pin of the wrench and the pinhole in the nut, you could use 1/64" clearance for pin sizes under 1/2 inch, 1/32 for 1/2 to 1 inch, and 1/16 for 1 inch and over. This does not come from a published standard, but rather my own (many years of) shop experience. Good luck.