1. Structure & Function
Design: Flat, circular metal ring with a central hole, no elastic deformation capability.
Purpose:
Distribute Pressure: Increase contact area to reduce surface pressure, preventing crushing or scratching of soft materials.
Compensate Misalignment: Adjust for uneven surfaces or hole deviations.

2. Applications
General Fastening: Essential for almost all bolted joints (e.g., steel structures, machinery).
Surface Protection: Shield soft materials (plastic, wood) or equipment from damage.
Pair with Spring Washers: Combined for anti-loosening (installation order: bolt → flat washer → spring washer → nut).

3. Standards & Specifications
Standards:
Chinese GB: GB/T 97.1 (standard series), GB/T 97.2 (large outer diameter series).
German DIN: DIN 125 (general-purpose), DIN 9021 (oversized outer diameter).
Sizing: Matched to bolt diameter (e.g., M10 bolt → 10.5mm inner diameter, 20mm outer diameter washer).
Materials: Carbon steel (zinc-plated, black-oxidized), stainless steel (A2-70, A4-80), brass, or nylon (special cases).

4. Pros & Cons
Pros:
Low cost, universal compatibility, no installation orientation required.
Protects surfaces and reduces wear/corrosion risks.
Cons:
No Anti-Loosening: Requires pairing with spring washers, lock nuts, or threadlocker.
Thickness Limitations: Too thick may affect clamping force; too thin reduces pressure distribution.

5. Usage Notes
Selection Guidelines:
Inner diameter slightly larger than bolt diameter (to avoid interference).
Outer diameter must cover the contact area (ensure even pressure).
Avoid:
Ultra-high-strength bolts (risk of washer deformation).
Dynamic loads without anti-loosening components.

Summary: Flat washers are foundational components in bolted systems, ensuring even load distribution and surface protection. While they lack anti-loosening capabilities, they are indispensable for reliable fastening in mechanical, construction, and industrial applications.