The weld nut is kind of nut specifically designed to be welded to another object. The common weld nuts are hex weld nuts and square weld Nuts.

The types of weld nut are;

• Round base nuts - These nuts have a long threaded cylinder with a large circular base to make welding easy. They also sometimes have projections (known as weld nibs or bosses) to keep the nut from warping while welding with a high current.
• Slab base nuts - These are very similar to the round base nuts, but with an obround, or slab shaped, base. These are used in channels, tubes, or other tight quarters.
• Tab base nuts - Tab base nuts are designed for spot welding on flat workpieces. They have a locating boss around the threads to locate it in a pilot hole.
• Hex & square nuts - These nuts are very similar to standard square or hex nuts, but have a locating boss and welding projections. The bosses also keep weld spatter out of the threads.
• Retainer weld nuts - Retainer weld nuts, also known as bridge weld nuts, have a floating nut retained inside a retainer to compensate for inconsistencies. The retainer is welded to the work piece while the nut is allowed to float.
• Tube end nuts - Tube end nuts are sized to fit into the end of standard sized tubing, thus creating a threaded tube from standard stock.
• Twin Piloted Nuts - Dual hole or twin piloted nuts are designed for use where there is a need for tapped holes close together.
• Four Projection Weld Nuts - Four projections designed to fuse simultaneously so each projection flows and seats properly.
• Single Tab Weld Nuts - Single button projection weld nut for use on heavier gage materials.

The weld nuts, also know as spot weld nuts, are fasteners that have a special surface area for welding to the mating material. Aluminum, steel and stainless steel weld nut are three of most common types, providing the strength need for given application. The common used of weld nut is in automotive industry.