The way I paint the bolts is I get a length of lumber, doesn't matter what kind or how long, mine board is a 2 x 6, 18 inches long.
Drill holes in the wood about 1/2 to 3/4 inch deep, with a 3/8 drill bit, that should be the right size for most of your bolts, drill holes around the board.
Place bolts to be painted in the holes and spray on the primer, then the paint.
You can do as many bolts at a time as you want.
Hope that is helpful.
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