A hex nut is a six-sided fastener with internal threading designed to mate with a bolt to secure materials together. Its shape provides excellent grip for tools like wrenches, making it one of the most commonly used types of nuts in construction, automotive, machinery, and manufacturing. Hex nuts are paired with bolts and screws to create secure and reliable joints. They are available in a wide variety of sizes, materials, and finishes to meet specific strength and environmental requirements.

Choosing the right hex nut size depends on the diameter, thread pitch, and length of the bolt or screw it's paired with. For compatibility, the diameter and thread pitch of the nut must match those of the bolt. The height of the nut also affects the strength of the connection, as larger nuts provide more surface area for threading. Typically, metric measurements are used globally, while standard measurements are common in the U.S. It's crucial to consult a sizing chart or engineer's specifications for load-bearing requirements.

There are several types of hex nuts, each serving different purposes. Regular hex nuts are for general fastening, while heavy hex nuts are thicker and provide extra strength. Lock nuts have built-in mechanisms, like nylon inserts, to prevent loosening in high-vibration environments. Jam nuts are thin and are often used as secondary nuts to prevent the main nut from loosening. Flange nuts have a built-in washer that helps distribute load evenly. The choice depends on factors like load requirements, environmental conditions, and vibration.

Hex nuts follow specific standards like ISO (International Organization for Standardization), ASTM (American Society for Testing and Materials), and DIN (Deutsches Institut für Normung) for size, strength, and materials. Grades, such as Grade 2, 5, and 8 for steel nuts, indicate different strength levels. Grade 2 is suitable for light applications, while Grade 8 is used in high-strength applications. Stainless steel hex nuts are often graded by their alloy type (e.g., A2 or A4), where A4 offers higher corrosion resistance, ideal for marine use.