Fasteners really should be created at the nominal size, it avoids a lot of confusion. Two reasons for this, first, these types of fasteners, with the exception of dowel pins, rarely go into close toleranced holes, and second, until KC has a sophisticated automatic tolerance handling, users aren't using the modeled bolt size to calculate a hole tolerance anyway. Even for dowel pins, I'd rather model the pin and the hole nominal, and set the tolerance when dimensioning. If you model an oversize dowel pin pressed into a nominal hole, the edge of the hole disappears in an isometric HLR or HLD drawing view, not what you want.