Zinc coating, passivation, anti-friction coating
A) Zinc-plated, yellow-chromated (generally referred to as “zinc yellow passivated” or simply “yellow passivated”)
B) Zinc-plated, transparent passivated (generally referred to as "bright zinc-plated")
1. The application of a zinc layer protects the material of the screw from corrosion and at the same time gives it a greyish silver finish.
2. The application of a passivation layer to the zinc-plated surface of a screw results (depending on the chemical process used) in a yellowish or transparent colouration of the metal. Passivation of the zinc layer improves corrosion protection.
3. Following the zinc coating and passivation processes, the screws are given a further (synthetic) anti-friction coating that reduces the driving torque required and makes the screws easier to use. SPAX with a zinc-plated finish are for indoor use. They should not be used outdoors or in damp locations.