Hex nuts are to be used with machine bolts to adhere facing materials to prevent tension and shear movement. Specifically in wood to wood, wood to metal, or metal to metal applications. Zinc grade 2 steel hex nuts are recommended for most general uses and are corrosion resistant. Be sure to pre-drill any holes and to use washers and bolts that are a similar grade and finish.
Hex nuts are for general applications and are used with bolts and washers of the same finish. The most commonly used nut, they are often found in deck and fence building. The called out size is the inner diameter and the number of threads per inch or thread pitch.