Although the function of all flat washers is to distribute the load of a threaded fastener, the type of washer you need depends on the specific application and the bolts being used. In the US, your primary choice is between washers conforming to SAE (Society of Automotive Engineers) or USS (United States Standard) standards. Choose wisely, because using washers of the wrong type or dimensions can compromise the integrity and safety of the connection.

SAE vs. USS flat washers: More than size matters

SAE washers are typically smaller and thinner than USS washers, with a smaller inside diameter. They're designed for use with SAE bolts, which are also smaller than USS bolts. SAE washers are commonly used in automotive and mechanical applications, where the available space may be limited.

USS washers, on the other hand, are larger and thicker than SAE washers, and have a larger inside diameter. They're designed to be used with USS bolts, which are larger than SAE bolts. USS washers are commonly used in construction and industrial applications, where strength and durability are important.