Tapping & Pipe threading

Hot-dip galvanizing adds a measurable thickness to the original steel. When threaded parts are galvanized, they require special attention to ensure that the fastener systems (nuts, threaded holes and bolts) fit correctly with this additional width.

Holes need to be overtapped (enlarged) in order to accommodate the increased size of the fastener. Tapping-off nuts is offered to a maximum diameter of 1 to 1/4”. If a galvanized bolt is being used, it should be re-tapped oversize.

While re-tapping the nuts after galvanizing results in an uncoated female thread, the galvanized male bolt provides cathodic protection and shields both components from corrosion. 

Overtapping Guidelines for Nuts and Interior Threads:

Nominal Nut Size (inches) and Pitch Oversize Dimension Requirement
½” – 1” NC + 1/64” O.S.
1 1/8” – 1 ¼” NC + 1/32” O.S.

*Pipe threading is offered up to a maximum diameter of 2” and must be single random in length.

Please contact Daam Galvanizing for additional information on our services and pricing.