The steel acorn nut has a black oxide finish. The acorn nut, also called a cap nut, has a domed top that covers exposed threads on rods, studs, and bolts. Steel is often used in applications where strength is the primary consideration. The black oxide finish offers mild corrosion resistance and lubricity.

Nuts are internally threaded fasteners that are used with bolts and threaded rods and studs to connect components. Several different nut styles fit a variety of application and installation requirements. Some styles, such as hex nuts, acorn nuts, flange nuts, and coupling nuts, must be tightened with a tool. Others, such as eye nuts, thumb nuts, and wing nuts, can be tightened by hand. Nut styles such as locknuts and self-locking hex nuts have a locking mechanism that makes them suitable for applications with a high amount of vibration.