This is a high-corrosion-resistant steel washer that is black and zinc-nickel coated, with an internal diameter of 6.4mm and manufactured to DIN 9021 standards, meaning it has a large outer diameter for better load distribution. It is designed for applications requiring enhanced durability and corrosion protection, and is a good visual and functional match for fasteners with a similar finish. 

Specifications and characteristics

• Standard: DIN 9021, which indicates a washer with a large outer diameter compared to standard flat washers.
• Material: Steel, which provides strength and wear resistance.
• Coating: Zinc-nickel, black finish (ZNBH or ZNBHL), which provides high corrosion resistance, suitable for wet environments and applications with high corrosion risk.
• Internal Diameter (ID): 6.4mm (often designated as an M6 size).
• External Diameter (OD): Because it's a DIN 9021 washer, the outer diameter is significantly larger than the inner diameter, designed to spread the load over a wider area.
• Purpose: To distribute the load of a fastener over a larger area, reduce vibration, and prevent damage to the mating surface.

Applications and benefits

• Corrosion resistance: The zinc-nickel black coating offers superior corrosion resistance compared to standard zinc plating.
• Durability: Made from steel for strength and durability.
• Visual matching: Designed to complement screws and nuts with a similar black, zinc-nickel finish.
• Load distribution: The large OD of the DIN 9021 standard is ideal for use with soft materials like plastic or for preventing bolt heads from sinking into the surface it's fastening.