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.
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.
Frequently Asked Washers Questions
What Do M10, M12, M20, M8, and M16 Mean When Referring to Washers?
The terms M10, M12, M20, M8, and M16 refer to the size of the washer, specifically the diameter of the hole that the washer fits over. These are standard measurements used in fasteners and washers, and they correspond to the metric thread sizes for bolts or screws.
- M10: Refers to a washer that fits a bolt or screw with a 10mm diameter.
- M12: Refers to a washer that fits a bolt or screw with a 12mm diameter.
- M20: Refers to a washer that fits a bolt or screw with a 20mm diameter.
- M8: Refers to a washer that fits a bolt or screw with an 8mm diameter.
- M16: Refers to a washer that fits a bolt or screw with a 16mm diameter.
These "M" values represent the nominal diameter (in millimetres/mm) of the threaded part of the bolt or screw. The corresponding washers are made to fit these bolts or screws snugly to ensure proper load distribution, secure fastening, and protection of the material being fastened.
So, when selecting a washer for a specific application, it's important to choose the correct size that matches the diameter of the bolt or screw being used to ensure optimal performance.
What Is The Best Washer For Use With Soft Materials Like Wood?
For soft materials like wood, washers with a larger surface area, such as square washers, are ideal. These washers distribute the clamping force more evenly, preventing the bolt or nut from pulling through the material or causing compression damage to the surface.
