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Re: Q: Hot-Dip Galvanizing of A 307 Bolts and Related Nuts

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Hot dip galvanizing A307 and A325 bolts is quite common for industrial structures especially in the power and petrochemical industry.  For treaded parts you would need to call out ASTM A153 where the items are centrifuged to remove excess galvanizing and also ASTM A563 for the nuts which requires that the nuts be tapped after coating.

I have specified mechanical galvanizing in the past for some special client requirements which is covered by ASTM B695.  I am not surprised that this is a special order and I would also expect it to be rather expensive.  In this process the items are normally pickled in a copper solution then tumbled in a zinc solution with glass beads.  Note that mechanical galvanizing will not be as thick as hot dip.

Zinc electroplating is covered by ASTM B633 and is commonly used by the post installed anchor companies.  It is very thin and not suitable for long term exterior exposure.

Thomas Hunt, S.E.
ABS Consulting

"Bill Polhemus" <bill(--nospam--at)>

12/08/2003 09:09 AM

Please respond to

Q: Hot-Dip Galvanizing of A 307 Bolts and Related Nuts

I have a job going for purchasing. I got shop drawings on miscellaneous steel which will be connected to some timber members using A 307 bolts.
The bolts were shown on the shop drawings as “hot-dip galvanized.” I changed it to read “mechanically galvanized.” Now the supplier claims it will take them over a week to get those.
The contractor wants me to “handle it” (implying “use hot-dip galvanized bolts”). I am uncomfortable with this because of past reading where hot-dip galvanizing of bolts caused fit-up problems and heat-related problems with the bolt material.
However, A 307 is not considered “high strength” I believe, so it may be all right to hot-dip galvanize.

Comments, please.


William L. Polhemus, Jr. P.E.
Polhemus Engineering Company
Katy, Texas USA