What is a Washers?

Simply put, a washer is a thin, disc-shaped ring with a central hole, typically made of metal (such as carbon steel, stainless steel, or copper) or non-metallic materials (such as rubber, plastic, or asbestos). It is placed between the head of a bolt/nut and the surface of the workpiece, or at the junction between the nut and the bolt.

Think of it as a "protective pad" or "buffer sheet" — while it doesn't directly generate clamping force, it ensures the entire fastening system is more reliable and durable by filling gaps, distributing pressure, or providing friction.

The Two Core Functions of Washers

The functions of washers can be grouped into two main categories, corresponding to the two most common types:

1. Anti-Loosening — Representative: Spring Washer

• Principle: A spring washer is an open, slightly inclined ring. When flattened between the bolt and nut, it generates a continuous elastic force. This force increases the friction between the thread pairs, effectively resisting loosening caused by vibration or impact.

• Intuitive Understanding: Think of it as a compressed spring that constantly "pushes" against the nut, making it reluctant to turn.

2. Protection and Pressure Distribution — Representative: Flat Washer

• Principle: A flat washer is a plain, flat ring. It has two main functions:

  • Increasing contact area: Distributes the pressure from the nut or bolt head over a larger surface area of the workpiece. This prevents softer materials (such as aluminum, plastic, or wood) from being crushed or damaged.

  • Surface protection: Prevents the nut or bolt head from directly rotating against and marring the workpiece's surface coating or finish during tightening.

Key Points for Selection and Use

1. More isn't always better: Many people default to the "bolt + flat washer + spring washer + nut" four-piece combo, but this isn't necessary in all cases. Whether a washer is needed, and which type, depends on the specific working conditions.

   • If the workpiece material is very hard (e.g., high-hardness steel) and the surface is already smooth and flat, a flat washer may not be required.

   • If vibration is extremely severe, a spring washer has limited effectiveness. In such cases, more reliable anti-loosening methods like nylon lock nuts or anaerobic adhesives should be considered.

2. Match hardness properly: The hardness of a flat washer should be moderate. If the washer is much softer than the nut or workpiece, it will crush and fail; if it's too hard, it may not conform to uneven surfaces. Generally, standard grades (e.g., those specified in national standards) should be followed.

3. Don't over-tighten rubber washers: For sealing rubber washers, tightening torque must be carefully controlled. Over-tightening will cause excessive deformation, loss of elasticity, or even cracking, leading to leakage.