Hex nuts can be used with all types if machine-thread fasteners including anchors, bolts, screws, studs and threaded rod. The hex nut is used with other fasteners – typically a bolt – to close or complete a fastening.
A square nut, or square head nut, is a four-sided nut that is designed for use with a square head bolt and flat washer.
Square nuts are typically used where there is an inset or channel in the receiving surface, such as in furniture, railroad applications, or other metal assemblies. The larger surface area of square nuts allows them to more easily resist loosening.
Traditional nuts simply consist of a basic threaded hole, so constant exposure to vibrations can knock them loose from the bolt on which they are placed. Lock nuts protect against loosening, however, by featuring a design that increases the nut's resistance to vibrations.
