Hot-dip galvanized nuts cannot be used on a plain finish bolt. Hot-dip galvanizing adds between 2 – 6 mils (. 002” – . 006”) of zinc to the threads of the bolt and due to this increased thread thickness, hot-dip galvanized nuts are tapped oversize to accommodate and create a workable fit. If you were to ever try to use a black nut with a galvanized bolt you will find that they don’t fit. The same is true with stainless nuts. That is because galvanized nuts are tapped oversized after they are galvanized to accommodate the extra thickness of zinc on the threads of the bolt.
A zinc plated nut would not fit properly on a galvanized bolt. Grade 5 is the most common grade used in manufacturing assembly. Galvanized plating protects the bolt from corrosion; typically used in outdoor applications. Hot dip galvanizing can only be done in a galvanizing plant. Site application is not possible. The colour of the zinc coating can be changed only by painting. The dimensions of the component or structure are limited by the size of the zinc bath.
As mentioned, pre-galvanized components are usually only immersed in the galvanizing bath for a very short time, resulting in a relatively thin coating. The thicker zinc coating produced by hot dip galvanization offers improved rust and corrosion protection versus pre-galvanization. The big difference is thickness: zinc plating is normally 0.2 mils thick. Hot dip galvanizing might be 1.0 mil thick – you get over 5 times the protection with galvanizing.
