Available Washer Types
The Engineering Function of Washers
While often seen as secondary components, washers are essential for the longevity of a bolted joint. Their primary purpose is to distribute the clamping load of a fastener over a larger surface area. This prevents the bolt head or nut from "digging into" and damaging the parent material, which is especially critical when fastening softer materials like aluminum, plastic, or wood. Most standard flat washers are governed by ISO 7089 or DIN 125.
Load Distribution & ID/OD
Washers are categorized by their Inside Diameter (ID), Outside Diameter (OD), and Thickness. A Fender Washer, for instance, has an oversized OD to distribute loads over very thin or weak materials, whereas a standard Plain Washer is sized to match the diameter of the bolt head or nut flange.
Spring & Locking Action
Specialized washers like Spring (Split) Washers or Wave Washers act as axial springs to take up slack caused by vibration or thermal expansion. However, in high-vibration critical joints, engineers often prefer Wedge-Locking washers (like Nord-Lock) which use tension rather than friction to secure the fastener.
Design Tip: Hardness Matching
Always ensure the hardness of the washer is compatible with the fastener. If you use a high-strength Grade 10.9 bolt with a soft, low-carbon steel washer, the washer may collapse or "dish" under the high clamping force, leading to a loss of preload and potential joint failure.