These screws are for winter draining of the seacocks for boats stored in-water. They should NOT be used for tying bonding wires to. These are an odd size machine screw in a special bronze that are nearly impossible to get, even from Spartan. Bonding should be tied to the flange bolts only, not the drain plugs. Just because a couple of major builders did it wrong does not mean you need to as well.
If you have 30 year old drain screws that are bonded to I would leave well enough alone as the threads often fail when trying to get them out.
Hope this helps. Good luck with your projects!!