Ziplock Bag or Wax Paper?

Using automotive paint will hold up much much better then spray bombs by far. I pretty much use the same method to hold my bolts and screws as you demonstrated with the cardboard. When I get ready to paint a hood, trunk lid or what is going next, that is when I paint the bolts.

Use a six point socket and then wrap the bolt head with a round or two of masking tape, double back on the tape end on the bolt head makes easy to unwind the tape.....