Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Stainless fasteners for galvanized assembly?

In an exterior application, is the better practice to use stainless or hot dip galvanized fasteners on hot dip galvanized components? Are there thread issues associated with hot dip galvanized bolts and nuts?

David Nelson
architect - Piscataway, New Jersey
2006

It's best to use the same metal throughout when possible; that minimizes galvanic corrosion. Yes, galvanized coatings are thick enough that allowance must be made in the thread cutting. Feel free to follow up.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006

Another point perhaps less obvious than the avoidance of dissimilar metals is that SS fasteners have low tensile strength.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

2006

Using galvanized with galvanized avoids both thread tolerance and dissimilar metals issues. Galvanizing, when specified for fasteners, is part of the manufacturing process. End-user shouldn't buy uncoated ones and have them galvanized (a code violation in some applications).

An ordinary nut manufactured per ASTM A563, when hot dip galvanized (or mechanically plated zinc) has been specified, has overtapped and lubricated threads for use with galvanized bolts.

Ken Vlach [deceased]
- Goleta, California

Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

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