How to paint metal shelf brackets

I've bought 30 odd new shelf brackets, which are white (I think they're painted in a white gloss of some kind) .

I need to paint them black and I have some black Hammerite smooth spray paint to do this. However do I need to add a primer or something similar to get the paint to stick on, or is it just a case of doing 4 light coats as mentioned on the instructions? I'm concerned that the paint is going to be uneven and drippy as I don't think it'll take. They'll just be used indoors. I obviously want to avoid having to sand them all although I don't mind if it's just a light sanding, I guess it won't take that long.

Any advice appreciated!

Louis

 

I doubt a primer is necessary. It would be a good idea to lightly sand them first, either 220 grit sandpaper or rough them up with steel wool.