Flat Washers, Spring Washers and Locking Methods: What Each One Actually Does

Washers are small components, but they can influence bearing pressure, surface protection, spacing and assembly behaviour. The first step is to identify what the washer is expected to do in the joint.

FLAT WASHERS
A flat washer provides a bearing surface under a bolt head or nut. It can help distribute load over a larger area, protect the joined surface and bridge an oversized or irregular hole within the limits allowed by the design. Washer dimensions, hardness and material should match the bolt, joint and applicable standard.

SPRING AND SPLIT LOCK WASHERS
Spring-type washers have traditionally been used in many assemblies, but they should not be assumed to guarantee resistance to loosening in every vibration condition. Their effectiveness depends on the joint design, preload, surface hardness and service loading. Where loosening has serious consequences, the locking strategy should be selected from verified engineering requirements rather than habit.

OTHER LOCKING METHODS
Depending on the application, designers may use prevailing-torque nuts, all-metal locknuts, nylon-insert nuts within their temperature limits, chemical threadlocking compounds, tab or locking plates, safety wire systems, wedge-locking washers or other engineered solutions. Each method has its own installation rules and reuse limitations.

PRELOAD IS CENTRAL TO A BOLTED JOINT
Many properly designed bolted joints rely on maintaining sufficient clamp load. A locking feature does not correct poor joint design, insufficient preload, damaged threads or an unsuitable tightening procedure.

MATERIAL AND FINISH COMPATIBILITY
The washer should also be compatible with the bolt, nut and clamped materials. Using a soft washer under a high-strength fastener can cause embedment or loss of clamp load. Dissimilar metals in wet environments can contribute to galvanic corrosion.

PROCUREMENT CHECKLIST
Specify washer type, standard, nominal size, outside and inside dimensions where required, thickness, material, hardness or property requirement, finish and quantity. For assemblies supplied as a system, avoid mixing components from unrelated specifications unless approved.

For structural, rotating, pressure, automotive, rail or other safety-critical applications, use the locking and washer arrangement required by the governing design standard or equipment manufacturer.