Hex is short for hexagon, which means they have six sides. Hex nuts, also known as:  finished hex nuts, hex full nuts, are one of the most common nuts available.  

Hex nuts have an interior thread and and are used with anchors, bolts, screws, studs, threaded rods and on any other fastener that has machine threads.

The use of hex nuts provides a strong, secure join with the bolt that is able to withstand high wear, stress and strain. As a result, hex nuts and bolts are used in many industrial applications that require a strong join that will hold under high wear, movement and heavy loads. Common uses include machinery, engines, motors, industrial equipment and furniture. Lock washers may used with hex nuts.