How to distinguish Galvanizing,HDG,Elcto-galvanizing in fasteners industry?

Lots of types surface treatment.If you were engineer in fasteners industry,how do you choose them .and do you know difference of galvanizing HDG elcto galvanizing finish way?We can tell you the technology difference,although we are not the manufacturer surface treatment,but we are manufacturer of fasteners.And do you know the difference?