A 1/4-20 Wellnut, also known as a nut insert or expansion nut, is a type of fastener that is used to attach objects to thin or hollow materials, such as sheet metal, plastic, or fiberglass. It consists of a flanged neoprene bushing with a threaded nut embedded in the non-flanged end. The flange helps to distribute the load of the fastener and prevent it from pulling through the material.
The 1/4-20 Wellnut has a thread size of 1/4-20, which means that it can be used with a 1/4-inch bolt with 20 threads per inch. It has a grip range of 0.250 to 0.457 inches, which means that it can be used to fasten materials that are between 0.250 and 0.457 inches thick.