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Oversize tap for anodizing

We have various products that require anodizing after the part has been tapped. Currently we use a labor intensive process to plug the holes so they don't get anodized. Is there a tap that would cut 4-40 threads slightly oversized so that when they are anodized the screw would thread correctly?

Brent Peterson
ME - Salt Lake City, Utah, USA
2004

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Threads should NEVER be anodized. The "cutting edge" of the thread is turned into pure Aluminum Oxide which is brittle, has no strength , and will crack right off when the mating threads are turned against it.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004

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While I don't doubt that there are MANY threads for which what Mr. Probert said is correct, my company has bulk anodized thousands of pounds of threaded products per year and never had any complaints regarding loss of functionality after anodizing. To answer Mr. Peterson's question, they do make oversized taps to allow for added material post-processing, they are marked by the Gage Number (H#) and are measured in 0.5 thousandths increments. According to one of my customers you should probably look into a H3 or H4 for that size of threads.

Jim Gorsich
Compton, California, USA
2004