Washers

Description

Washers are thin disk-shaped plates with a central hole which are used to distribute the weight of a threaded fastener. Generally, washers are made of plastic or metal. Metallic washers are made of materials including titanium, stainless steel, hardened steel, steel, spring steel, nickel-based alloy, copper, bronze or copper-based alloy, brass, and aluminum. Non-metallic washers are made of rubber, PTFE, PVC, polypropylene, polycarbonate, polyethylene, nylon, polyester, felt, leather, acetal, and asbestos. Surface coatings/treatment provided for washers include zinc chromating, zinc plating, tin plating, nickel plating, galvanizing, phosphating, black oxiding, and anodizing. The outer diameter (OD) of a washer is generally around twice its inner diameter (ID). Washers play an important role in preventing galvanic corrosion.

Types

The various types of washers are:

• Flat washers
• Lock washers
• Split washers
• Belleville washers
• Wave washers
• Spring washers
• Bimetal washers
• Fender washers
• Spherical washers
• Star anchor washers
• Phenolic washers
• Shoulder washers
• Multi-tooth (star washers)
• Bit guard (horse tack) washers
• Special purpose washers
• Crank washers
• Tab washers
• Taper washers
• ID Hex washers
• Torque washers
• Square washers
• Sealing washers
• SAE washers
• Finishing or countersunk washers
• D-shaped washers
• C-shaped washers
• Beveled washers

Specification

Washers are specified in ANSI metric sizes or ANSI nominal sizes. The specifications for washers are: 

• Rated or working load
• Working or thickness height
• Outer diameter
• Inside diameter
• Screw pitch thread
• Nominal screw sizes

Applications 

Washers have a wide range of applications such as:

• Washers are used as a locking device, preload indicating device, wear pad, spring, and spacer
• Silicone or rubber washers are used for reducing vibration during fastening of fans to computer cases
• Rubber washers are utilized in taps, where they seal the flow of gas or liquid