Presstech, India

A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener. Other uses are as a spacer, spring (belleville washer, wave washer), wear pad, preload indicating device, and locking device. Usually washers have OD (outer diameter) about twice their ID (inner diameter).

Washers are usually metal or plastic. High quality capscrews require hardened steel washers to prevent the loss of pre-load due to Brinelling after the torque is applied. Rubber or fiber gaskets used in taps to stop the flow of water are sometimes referred to colloquially as washers; while they may look similar, however, washers and gaskets are usually designed for different functions and made differently.

Types 

• Anchor plate : An anchor plate or wall washer is a large plate or washer connected to a tie rod or bolt. Anchor plates are used on exterior walls of masonry buildings, for structural reinforcement. Being visible, many anchor plates are made in a style that is decorative.

• Belleville washer : A Belleville washer, also known as a cupped spring washer, is a type of non-flat washer. It has a slight conical shape which gives the washer a spring characteristic. Belleville washers are typically used as springs, or to apply a pre-load or flexible quality to a bolted joint. Belleville springs are also used in a number of landmines e.g. the American M14 mine.

• Spherical (Self-aligning nut) : A spherical washer is a washer with one radiused surface, which is designed to be used in conjunction with a mating nut in order to correct for up to several degrees of misalignment between parts.

• Torque : A torque washer keeps the carriage bolt from spinning freely. It has a square hole in the center where the carriage bolt square fits into. It also has several bent prongs around the edge that dig into the wood to keep the washer from spinning.

• Washer nut : The washer nut is a combination nut and washer. The washer is free floating just like using a separate washer and nut, however assembly is easier because the washer is captured.

• Other : Flat,fender washer (mudguard washer in UK),hardened,lock,split,phenolic,wave,shoulder,spring,Multi-tooth (star washers),Bimetal,bit guard (horse tack).