Are the threads of a galvanized anchor bolt cut undersize?

No. A galvanized anchor bolt will have a coating of zinc on the threads that typically varies from 2 – 6 mils (thousandths of an inch). Therefore, black (plain finish) and zinc plated nuts will not thread onto a galvanized bolt. Instead of cutting the threads undersize so nuts will fit, hot-dip galvanized nuts are tapped oversize to accommodate the zinc on the threads of a galvanized anchor bolt. ASTM A563 specifies the amount a nut should be tapped oversize when being used with a galvanized bolt.

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