bolt size for A body bumper bracket

Does anyone know the size of the bolt that attaches the front bumper bracket to the side of the front frame rail on a 72 Duster, there are 2 bolts that go into the frame rail, my bolts are long gone and i want to fabricate some casters to bolt up. want to pick up the bolts on the way home tonight,

thanks in advance,
340Kid

1/2 inch by 13 thread and however long you need

thanks,