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Galvanized Bolts and Chased Threads

Answer: No, externally threaded fasteners should not be “chased”. Chasing threads is a term used to describe re-cutting threads after galvanizing to remove excess zinc gained during the GALVANIZEING PROCESS. Reworking the threads can possibly remove the zinc coating and eliminate the corrosion protection of the threaded portion of the fastener. Chasing, if not performed with extreme precision, can also remove additional steel from the threaded portion of the fastener resulting in threads that are undersized and out of tolerance.

 ASTM F2329 is a relatively new specification that covers galvanized fasteners and supersedes A153. This specification (5.4.1) clearly prohibits the alterations of threads after galvanizing stating, “Fasteners that have been hot-dip galvanized shall not be further altered (such as subjected to a cutting, rolling, finishing-tool operation) by the galvanizer unless specifically authorized in writing…”

Portland Bolt’s custom galvanizing system is specifically designed for threaded fasteners and uses centrifugal force to clean the threads. After parts are removed from the galvanizing tank they are spun immediately following using a high-speed spinner. This process creates high quality galvanized threads and trouble-free nut fit. In addition, galvanized nuts are tapped oversize to accommodate the extra 2 – 6 mils of thickness that hot-dip galvanizing adds. The tolerance for tapping nuts is covered under A563.


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