> [bought bolts at Home Depot]
> I get them home, and WTF? =A0I finally realize what is wrong, and now I'm
> friggin' pissed because the bolts are worthless for my application. =A0Th= e
> unthreaded portion of the shanks are a full 3/64" shy of their stated
> diameters"!!! =A0Oh sure, the outside diameter of the threaded portion is
> 3/8", but the shanks aren't even close. =A0
Alas, that's normal. Unless you get 'shoulder bolts', the shank diameter is not the controlled 3/8" you want, because the threads weren't cut on a 3/8" blank, they were raised (rolled, it's called) on a subsize blank. You can build up the shank with welding, I suppose, or just roll a bit of sheet metal around the shank. Or scrounge in decades-old assortments of fasteners for an archaic example of what-you-expected.
Some high-strength fasteners will have the full shaft diameter, perhaps, because not all alloys are roll-able.
Shop with calipers.