Nuts are used with bolts, threaded rods and studs to fasten items together. When choosing a nut, there are several factors to consider. The first is type. Does the nut need to be one you can twist off with your fingers? Wing or thumb nuts, for example, allow this action. Does the nut need to lock into place? Self-clinching nuts or locknuts are just two of the types that have this capability. There are nuts used for spacing such as coupling nuts, and nuts that add a lifting point to your existing bolt or screw such as eye nuts.
The next consideration is material. Metals and alloys tend to be more durable, heat resistant and strong, but some can be susceptible to corrosion, while plastics are nonmagnetic and tend to be more chemical resistant.
The size of the nut should match the bolt. The size name reflects the external diameter of the bolt, followed by the threads per inch in standard nuts and millimeters per thread for metric nuts.