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Shims & Washers: What Sets Them Apart?

Shims and washers are two of the most basic tools in use in the aerospace and aviation industries. However, they both play an important role in any piece of machinery they’re found in. Both shims and washers are used to guarantee a part will fit properly, aid in flexibility, and improve the overall performance of a given part in a given application. Despite their similarities, shims and washers differ in function and application.

Shims are constructed in the shape of a wedge, tapered to easily fit into gaps between adjacent surfaces. Their chief purpose is to create a level surface or better support. The base material used to manufacture shims is called shim stock. The type of stock used is dependant on the planned application of the item. The materials commonly used to create shims include plastic, rubber, wood, stone, metals, layered paper and layered aluminum foil. Though these are the most common types of shims, there are many more specialized types such as laminated shims, calibration foil shims, and certified plastic shims.

Laminated stock is advantageous because it provides users with the ability to remove layers of the shim until the optimal size is found. Calibration foil shims are used to create a precise plastic coating thickness on an item, surface, or substrate, and come either single foil or layered. Certified plastic shims are a cost-effective alternative to metal shims when the application doesn’t necessitate the strength of metal shims.

Washers are made from many materials such as metal, plastic and rubber, and come in a huge variety of sizes. They are commonly in a disk-like shape with a hole in the middle for a screw or other fastener to be inserted. They improve function of machinery by acting as spacers, fitting, locking devices, vibration reducers, and wear pads. The three most common types of washers are plain washers, spring washers, and lock washers.

Plain washers are used to distribute weight, protect joined surfaces, and protect materials from corroding. Spring washers and lock washers have very similar functions, namely preventing connections from weakening or slipping apart. They put up with factors like weight change, pressure, movement, friction and vibration and are designed to be resistant to rotation. Lock washers are sometimes manufactured with teeth-like grips to further help prevent movement.