When we talk about washers we are entering into a wide category of fasteners that incorporate many types and varieties that are very different from one another and can serve very specific purposes. Starting out with the most common, when most people think of washers, in general we are talking about flat washers.
Flat washers, also referred to as Type A washers, are thin, flat, and circular general-purpose washers with a centrally located hole. Standardized flat washers may be designed by the use of imperial or metric dimensions. Standard imperial washers include SAE washers, for use with fine threaded nuts and bolts, and USS flat washers, for use with coarse threaded bolts and nuts. Standard metric washers are available in several gages as defined by JIS standards.Washers are measured and characterized by either imperial or metric design units.
The dimension of washers can be specified by standard nominal values, gaged values, or may be customized for particular applications. Nominal ANSI sizes refer to the size of the fastener that the washer is designed to mate with. Nominal SAE, USS, and JIS sizes not only specify the inner diameter of the washer but also dictate the outer diameter and thickness of the washer. For heavier duty applications Structural flat washers are appropriate.
Structural washers are ideal for heavy-duty applications. These washers are thicker than most flat washers, so they can withstand exceptionally high loads. Their build tends to mimic that of a standard flat washer.
Most structural washers also include a rigid finish. This design combined with their durable construction allows these washers to provide a secure hold—no matter the application. Structural washers are most commonly utilized in the construction industry but can be seen in other applications as well.
Fender Washers are another type of common flat washer. A fender washer, though similar in shape to a standard washer, differs in that the outside diameter is traditionally much larger in proportion to the center hole. With this design, a fender washer can be placed under the head of a bolt or nut to help distribute forces applied when tightening. Its oversized outside diameter also provides more bearing surface for the load of the fastener—distributing the load further on soft or thin materials. Fender washers are commonly used in automotive, sheet metal, plumbing and electrical applications. Flat washers come in many types of materials. Metallic materials of construction available for washers include aluminum, brass, copper base alloy or bronze, copper, nickel base alloy, spring steel, steel, hardened steel, stainless steel, and titanium.Non-metallic materials of construction include ABS, acetal, asbestos, felt, leather, nylon, polyester, polycarbonate, polyethylene, PVC, polypropylene, PTFE, and rubber.
Lock Washers, a locking washer is a type of washer that’s designed specifically to prevent the bolt with which it’s used from loosening. Like other washers, they’ll distribute the load of the fastened object or objects more evenly. Locking washers go one step further, though, by “locking” the bolts in place.
Bolts can loosen over time. If installed in a machine or piece of equipment, a bolt may gradually loosen. Eventually, the bolt may work its way out of the threading hole where it was originally installed. Locking washers prevent this from happening by securing the bolt in place. Even if the machine or equipment produces heavy vibrations, the bolt shouldn’t loosen if it’s secured with a locking washer. Locking washers work by exerting downward tension. When inspecting a locking washer, you may notice that it doesn’t have a complete circular shape.
While most traditional washers are circular, locking washers have a slightly different shape. They consist of a semi-raised piece of circular metal. In other words, locking washers feature a coiled design, which is responsible for their locking action.With their coiled design, locking washers work in a similar way as a spring. Springs, of course, exert tension when exposed to pressure. Locking washers share this characteristic trait by exerting tension as well. When you twist a nut onto a bolt, it will press against the locking washer. The locking washer will then generate tension that secures the bolt in place. There are a few different types of locking washers. A helical lock washer (also called a “split washer”) looks like a ring with uneven ends. The ends of the ring bite into fastener material to keep it from turning. Internal-tooth lock washers have teeth located on the inside of the ring and provide a good connection with small fastener heads.
External-tooth lock washers
External-tooth lock washers (also called a “star washer”) have the teeth located on the outside of the washer ring, which works well with large fastener heads. External-Internal/Combination lock washers have teeth on both the inside and outside of the ring. This provides better security with large fastener heads.
Wedge lock washer
Wedge lock washer are a two piece, pre-assembled, two piece wedge locking washer. The pair of joined washers feature cams on the mating face and ridges on the other. The two washers are joined with a mild adhesive on the cam side of the washer and installed between conventional threaded fasteners and a joining substrate. Wedge lock washers use tension to secure a joint rather than the frictional force that is applied by traditional washers.
Pyramidal-type lock washers
Pyramidal-type lock washers are used for projects requiring high-tightening torques. Countersunk lock washers are used with flat or oval head screws having either 82 or 100-degree countersunk angles.
Dome-type lock washers
Dome-type lock washers distribute load over a wide area and are recommended for use with thin or soft materials that require high torque for holding. Dish lock washers are similar to domed lock washers but can be used in applications requiring less torque or load. The most common materials for lock washers are aluminum, stainless steel, K-Monel, bronze, zinc, phosphor bronze alloy and carbon steel.
The material used in manufacturing the lock washer is important in preventing it from breaking down, thereby losing its fastening strength. You’ll find lock washers commonly used in applications involving vibration and possible slippage of fasteners. Industries that commonly use lock washers are the transportation industry (automotive, aircraft, marine), defense, agriculture, construction equipment, HVAC, and waste management among many others.