Need to know the difference between SAE and USS washers? Don't know what a fender washer is? Here's a quick guide to get you started on how to identify washers.

USS: Most common type of washer. It is used under the head of a bolt or nut. It has a larger outside diameter to help distribute the forces applied when tightening.

SAE: You see this type in the automotive industry quite often. It is very similar to the USS except that it has a tighter fit to the bolt and has a smaller outside diameter (that is the main difference).

FENDER WASHER: Fender washers have an over-sized outside diameter but are thinner and usually made with a cheaper material (as opposed to USS).

LOCK WASHER: Lock washers are used to help keep the nut from loosening from the bolt. When tightened, the lock washer "locks" the nut in place.

EXTERNAL LOCK WASHER: Has external teeth that help lock the nut in place.

INTERNAL LOCK WASHER: Has internal teeth that help lock the nut in place.

FINISHING WASHERS: Designed for a flush finish type screw (ie: Flat or oval head screw). The finishing washer has a distinct cup shape.

Well, those are the most common types of washers. There are several more with many different types of composition but these are the main ones that you will run into. I hope you find this information useful!