How much weight is gained from hot-dip galvanizing bolts?

Galvanized Hex BoltsAccording to the American Galvanizers Association (AGA) the weight of an item on average will increase about 3.5% from the zinc added during the galvanizing process. However, the AGA goes on to say, “…that figure can vary greatly based on numerous factors. The fabrication’s shape, size, and steel chemistry all play a major role, and other factors like the black weight, the different types of steel that get welded together, and the galvanizing bath chemistry can also have an effect.”

When considering galvanized fasteners this percentage is often lower. For example, the actual increase in the weight of a galvanized 1″ x 10″ A307 hex bolt compared to a plain hex bolt is approximately 0.26%. The zinc thickness requirement for hot-dip galvanizing threaded fasteners is covered by ASTM F2329. This specification states the average minimum coating thickness at 1.7 mils (.0017 in.). Overall the weight increase of fasteners due to zinc from galvanizing is fairly minimal.

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    @Akash- The industry standard per the AGA is 3.5%, however our testing on bolts shows that it adds less than 0.50%, but that will vary with the specifics of what is being galvanized and how thick the coating is applied.

    How much weight should I add to the weight of heavy hex bolts after galvanizing.
    We have a job that has a billion bolts on it and I should know this .
    Thank you for your help.

    @Edward – In our experience it adds less than one half of one percent (>0.50%). The actual will vary with the configuration of bolt and the thickness of the zinc coating.

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