Nuts and bolts are used in a variety of projects around the house. Most of the time, washers are needed on one or both sides to prevent slippage and provide proper spacing for the nuts and bolts. Different types of washers provide different advantages. Before reaching for a flat washer or a split washer (also known as a lock washer), it is important to know which you need for the specific task at hand.
While they're both types of washers, flat washers and lock washers actually have different purposes. Flat washers are used to increase the surface area in order to more evenly distribute the force applied with tightening the fastener. Lock washers are used as a means of creating tension during tightening in order to help keep the nut from working loose later.
There are a number of types of both flat and lock washers. Flat washers come in several different types including common flat, United States Standard (USS) flat and Society of Automotive Engineers (SAE) flat. There are also fender washers, which are thin with a wide body, dock washers which are thick and wide and a few other flat styles. Lock washers are similar; they come in the common lock variety as well as the much thicker high-collar lock style. Toothed lock washers are also available, in varieties that feature either external or internal teeth to secure them to wood or other materials.
Both flat and lock washers come in a wide variety of interior diameters, exterior diameters and thicknesses. Flat washers may be constructed from a variety of materials including brass, silicon bronze, stainless steel, zinc plated steel, chrome, rubber and many others. Lock washers may also be made from a number of different materials including stainless steel, zinc plated steel, silicon bronze, galvanized steel and many others.
Flat and lock washers may be used for a number of different applications depending on their size and composition. Silicon bronze washers are frequently used for marine projects, such as wood boat restorations, due to their strength and superior corrosion resistance. Zinc plated and galvanized steel washers can provide good protection against rust. Stainless steel is used for most common applications and chrome washers, with their high gloss finish, are used primarily in areas where they are intended to be seen.
Depending on what you're doing, the flat washer/lock washer/nut order on your bolt will affect how well the nut and bolt work. Flat washers may be used on either the bolt side, the nut side or both sides of the fastener. Flat washers help to distribute the force of tightening the nut by increasing the surface area. They may also be useful as spacers when a bolt may be a bit too long for the job. Lock washer use is a bit different as they are typically used on the nut side of the fastener. Lock washers are frequently used in applications that involve vibration which may tend to work the nut loose.