The 18-8 stainless steel machine screw hex nut has a black oxide finish and meets American Society of Mechanical Engineers ASME B18.6.3 specifications. Designed for use with machine screws, the nut has a flat top with a large bearing surface and chamfered corners. It has six flat sides that a wrench can grip to turn from the side, enabling use when there is no space above the nut. The 18-8 stainless steel material provides strength and offers good corrosion resistance in many environments. The material may be slightly magnetic. 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. Some nuts have a self-locking mechanism, such as a nylon patch or distorted threads, that makes them suitable for applications with a high amount of vibration.