Color of surface
Stainless steel screws are made of stainless steel. The color of stainless steel is mainly an alloy of iron and carbon, so the color is close to that of iron.
The surface of galvanized screws is galvanized with white zinc, color zinc, black zinc, etc., so the color of galvanized screws is generally white, color, and black.
The nickel-plated screws are uaually bright silver and metallic luster.
Alternative methods
Use magnets to distinguish. Stainless steel is generally not magnetic or weak magnetic so that stainless-steel screws cannot be attracted by magnets.
Use strong acid and strong alkali to distinguish. Stainless steel contains chromium and nickel, which lead to strong corrosion resistance and is not corroded by strong acids and alkalis.
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