A plain washer is a thin plate, which is most commonly has a disk-shape with a hole in middle. It is widely used to distribute the load of a threaded fastener. Plain washers are used to provide a larger bearing surface where screws, bolts and nuts come in contact with the bearing surfaces.
The main role of flat washers is to increase the size of a screw’s bearing surface area, and reduce the surface pressure applied on the fastened object.
Looseness can result when the bearing surface sinks under the surface pressure, so using a flat washer to reduce the surface pressure is very effective.
This is especially crucial if the contact area between a screw’s bearing surface and the object being fastened is small when fastening to a slot, for instance, or if the object being fastened is made of soft material such as aluminum or resin.
d1 Inside diameter
d2 Outside diameter
Incidentally, since flat washers are basically manufactured by pressing, one side has rounded corners and one side has burrs, as shown in the figure.
There is no fixed rule about which side goes up and which goes down, but given the issue of bearing surface pressure mentioned above, it’s more effective to put the burred side facing down.
However, since the burrs could mark the surface of the fastened object during tightening, it would be better to put the rounded side down if you want to avoid plating peeling.
There is a large range available to suit every application.
The normal series is available as per the following standards
JIS B1256 Normal Series
Smaller OD washers for Machine Screws are available as per the following standards.
JIS B1256 Small Series
Larger OD washers are used for irregular holes, softer materials and larger holes. They are sometimes referred to as “Fender Washers” and distribute the load over a larger area making them useful for materials such as wood and plastics.
These are available as per the following standards
JIS B1256 Large Series
Special dimensions are also available under our Penny Washer Series and we have a range of SHIM washers as per DIN 988.
We ensure that every batch confirms correctly to the relevant standard and material grade.
They are available in the following materials.
Mild Steel – Natural Finish, Zinc Plated and Nickel Plated.
Stainless Steel – AISI 304 and AISI 316
Titanium – Grade 2
Plain Washer Hardness
Class 100 HV : Minimum HV 140 (Rockwell B 56.2 minimum). Suitable for hexagon bolts and screws of product grade C in property classes up to and including 6.8; hexagon nuts of product grade C in property classes up to and including 6; case-hardened thread rolling screws
Class 140 HV : Minimum HV 140 (Rockwell B 75 minimum). Useful for majority of industrial applications including stainless steel assemblies.
Class 200 HV : Minimum HV 200 (Rockwell B 91.5 – C 29.8). Useful for higher demands in manufacturing, maintenance and repair.
Class 300 HV : Minimum HV 300 (Rockwell C 29.8- 40.8). Hardened and tempered. Best suited for use with through hardened screws, bolts and nuts.