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Yellow vs. blue chromated screws

Could some body explain the difference between yellow chromated and blue chromated screws please?

Nigel Tampling
hobbyist - Saarloius, Hessen, Germany
2004

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2004

Both screws are probably zinc plated. Historically, the yellow chromate is a heavier and more corrosion resistant coating, containing more hexavalent chromium, which will last longer before white rust than the blue chromate will, which has less or perhaps no hexavalent chromium.

However, the world has become brain dead (perhaps due to chromate poisoning), so today manufacturers are eagerly dyeing their blue, more benign, trivalent chromates yellow to render the more benign new parts indistinguishable from the toxic old parts. They claim to have their reasons :-)

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