Originally Posted by Bill Kapaun
8mm = .31496
5/16 = .31250
Difference is less than .0025"!! It doesn't make sense that one is too big and one is too small.
Sounds like something other than an Allen head.
I agree that this doesn't make sense. In most real world applications, 5/16" and 8 mm wrenches can be used interchangably. BTW, if a 5/16" is really too small, then a 7 mm will be even smaller so don't bother looking for one.