I started a thread months ago, about how to paint zinc plated bolts heads, to make sure the primmer would hold. I got lots of conflicting advice from both here and from other sources so I decided to experiment. I took three bolts and primed 1 with rattle can primer, 1 with commercial sandable automotive primer and one with PPG epoxy primer. Then, they were painted with Gillespie 24087. After a few weeks, I took an awl and tried to scratch them. The primer failed in all but the epoxy primed one. The primmer flaked off the other two but held on the epoxy. Just thought this may help others. I have now painted all my replacement bolts using epoxy primmer. Some nuts will need to be painted separately after installation. A picture of my bolt head paint board is below;