Washers
(5 Products)Washers are integral to creating reliable and durable bolted joints, acting as crucial intermediaries between the tightening element (bolt head or nut) and the substrate material being joined. During the tightening process, the rotation of the bolt head or nut can scratch, mar, or gall the surface of the material being fastened. A washer acts as a stationary protective barrier between the rotating fastener component and the substrate, preserving the surface finish and integrity.
What Are Washers?
Washers are used to distribute the clamping force generated by tightening a bolt or nut over a larger surface area of the joined material. When a fastener is tightened, significant stress is concentrated directly under the head or nut. Without a washer, this concentrated force can cause damage, such as denting, cracking, or localised yielding (brinelling), especially in softer materials like wood, composites, or thin sheet metals.
By increasing the contact area, the washer reduces the surface pressure, preventing such damage and maintaining the integrity of the joint. In high-quality, high-load bolted joints, hardened steel washers are essential to prevent the loss of preload (the initial clamping force) due to this Brinelling effect after torque is applied.
Square Plate Washers
Square Plate Washers are specifically designed to offer a large, flat-bearing surface, making them particularly effective for load distribution in timber framing, general construction, and heavy-duty applications where standard round washers may not provide sufficient coverage.
Available Sizes
We stock Square Plate Washers in the following metric sizes, designed to fit the corresponding bolt diameters :
Understanding Washer Sizing
- Inner Diameter (ID): The most critical dimension for compatibility is the washer's inner diameter (hole size). This ID must be correctly matched to the nominal diameter of the bolt or screw it will be used with. The washer's ID is typically slightly larger than the bolt's nominal diameter to allow it to slide onto the bolt shank easily without excessive play. Using a washer with too small an ID will prevent assembly, while one with too large an ID may not seat correctly or provide adequate bearing surface under the head/nut.
- Outer Diameter (OD): The outer diameter determines the washer's bearing surface area. The required OD depends on the application, the material being fastened, and any space constraints. Standard plain washers have a typical OD (often around twice the ID), while fender washers have a significantly larger OD for wider load distribution. Narrow or wide series washers (e.g., ANSI Type B) offer variations for specific needs.
- Thickness: Washer thickness influences its strength, stiffness, load distribution capability, and spacing function. Standard washers have defined thicknesses, while heavy-duty types like structural washers (ASTM F436) or dock washers are significantly thicker.
- How to Specify/Select: Always select the washer based on the nominal diameter of the bolt or screw it is intended to fit. Consult dimensional standards and size charts specific to the washer type (e.g., plain, fender, structural) being considered. Be mindful of different series or forms within a standard that affects OD and thickness.
