A washer is a circular piece of hardware that evenly distributes the force of a screw or nut. Washers can relieve friction and prevent corrosion or leakage. They can help maintain tension or serve as a spacer. This wide range of applications makes washer a necessity in most construction projects. However, choosing the right type of washer for a project can be more complicated than it seems. This guide will cover the types of washers and their recommended purposes.
Washer Materials and Types
Washers are made from a variety of materials. The most common are galvanized carbon steel and stainless steel. Carbon steel is stronger than stainless steel. However, stainless steel will not rust or corrode like carbon steel can. Other metal washers include zinc, copper, brass and iron. Specialty washers include plastic washers, rubber washers, ceramic washers and phenolic washers.
The three main types of washers are plain washers, spring washers and lock washers. Specialized washers exist within these categories that serve unique purposes.
Tip: Washers (as well as nuts) are sized in both U.S. and metric measurements.
Also called flat washers, plain washers are the most common type of washers. They distribute pressure and protect the object to which the screw or nut is fastened. If a hole is too big for the fastener, a plain washer can be used to correct the size difference.
- Also known as Type A plain washers. The flat washer is what most people picture when thinking of a typical washer. They are circular and flat with a central hole to accommodate a bolt. Flat washer come in varying thicknesses.
- Application: Used to distribute force or correct a hole size. Good for general use.
- Named for their common use on car fenders. Fender washers are flat washers with a small hole and comparatively large outside diameter.
- Application: Used to distribute force over a large surface area, usually thin metal.
- A torque washer has a square hole and outer prongs that prevent its accompanying bolt from spinning while a fastening a nut.
- Application: Used with a carriage bolt for woodworking projects.
- Resembles a flat washer, but it has a slot cut from the center hole to form a “C” shape.
- Application: Used any time a washer might need to be removed, adjusted or replaced without removing the fastener.
- Also known as a countersunk washer. A finishing washer has a sunken top designed to catch the fastener.
- Application: Creates a flush surface when secured with countersunk screws.
Spring washers have axial flexibility that allows them to move with vibrations. Their flexibility keeps them from getting loose or coming unfastened due to those vibrations. They increase the elastic properties of a joint.
- Sometimes called a conical spring washer. The belleville washer has beveled sides that support heavy force with small deflections.
- Application: Used for projects that involve thermal expansion.
Crescent Spring Washer:
- Also called curved spring washers. Crescent washers look like flat washers that have been slightly curved to exert light pressure and maintain flexibility.
- Application: Used to absorb movement.
Dome Spring Washer:
- Dome spring washers look like belleville washers but have rounded sides.
- Application: Used wherever you would use a crescent spring washer but also need to create a flatter surface.
Finger Spring Washer:
- Finger spring washers have three curved flanges.
- Application: Used for dampening vibrations and noise.
Wave Spring Washer:
- Wave spring washers are curved in two directions, creating a wave-like shape.
- Application: Used most often as cushions or spacers.
Lock washers secure fasteners that might otherwise rotate or lose friction.
- Sometimes called helical washers. Split lock washers are non-continuous rings that have each end bent slightly outward in opposite directions. Split lock washers flatten when they're secured. Each end digs into the mating surfaces.
- Application: Used to lock a fastener into place.
- An external tooth lock washer has several teeth on the outside diameter that bite into one surface and resist compression.
- Application: Used to lock wide-headed fasteners into place.
- An internal tooth lock washer has several teeth on the inside diameter that bite into the fastener.
- Application: Used to lock shallow-headed fasteners into place and absorb shock and vibrations.
Different types of washers are suitable for different jobs. As you choose between them, consider the washer's applications and the type of nut or other fastener that will be used.
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