The authoritative public forum
  for Metal Finishing since 1989
-----

Metric Blue or Yellow Zinc

I am trying find documentation to discern whether Standard "Metric Blue" coating/plating on Steel Nuts and Bolts exceeds the standards that are set for Standard Metric "Yellow Zinc" Nuts and Bolts.

Tom Trahan
aerospace - Hattiesburg, Mississippi
2006

---

That's a good question, Tom. I could be wrong, but my understanding is that decades ago when metric fasteners were still a rarity, the hardware manufacturers started dipping the screws and nuts with metric threads into "metric blue" dye merely to make them quickly distinguishable from similar sized ANSI fasteners. To the best of my knowledge the blue dye did not indicate any special strength or tolerance, but I'd be curious if my understanding is correct.

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

---

February 15, 2011

Having worked for the company (Metric Blue) I can tell you that at one point, the blue offered a certain level of corrosion resistance, however in the final years of the company, the blue was solely a means of identifying the product as a metric fastener.

Metric blue was offered in 8.8, 10.9 and 12.9 hex head cap screws, and 12.9 socket head cap screws, so the colour itself did not reflect any strength.

100% for NAAMS standards.

Hope this helps,

C O'Neil
- Ottawa, Ontario Canada