Glossary of terms

Annealing Heating and slow cooling to remove stresses, make steel softer, refine the structure, or change its ductility.

Carburizing Adding carbon to the surface of iron-based alloys by heating the metal below its melting point in contact with carbon-rich solids, liquids or gases.

Cyanide Hardening A method of case hardening which brings the metal surface in contact with the molten cyanide salt followed by a quenching.

Decarburization Removal of carbon from the surface of steel. This can occur through normal oxidizing action or as the result of heat treatment.

Drawing (Tempering) Reheating after hardening , held at a specific temperature and then quenched. This reduces hardening and increases toughness.

Hydrogen Embrittlement A condition where the surface finishing of metal (plating) results in a brittle outer case due to immersion in acid. Baking immediately following the plating process removes this brittle surface condition.

Nitriding A hardening process which adds nitrogen to a metal surface through contact with ammonia gas. Produces surface hardness (case) without quenching.

Precipitation Hardening A hardening process where certain metals are held at elevated temperature without quenching (age hardening).

Quenching Rapid cooling of steel by immersion in oil or water to fix its structure in a hardened state.

Sphereoidizing (anneal) Any process of heating and cooling steel that produces a rounded or globular form of carbide. This softens the metal, improving ductility.

Stress Relieve A low temperature heat treatment which removes stresses caused by cold working.

Thread series

Coarse Thread Series Applications

The coarse thread series (UNC/UNRC) is generally used for the bulk production of screws, bolts, and nuts. It is commonly used in relatively low strength materials such as cast iron, aluminum, magnesium, brass, bronze, and plastic because the coarse series threads provide more resistance to internal thread stripping than the fine or extra-fine series. Coarse series threads are advantageous where rapid assembly or disassembly is required, or if corrosion or damage from nicks due to handling or use is likely.

Fine Thread Series Applications

The fine thread series (UNF/UNRF) is commonly used for bolts and nuts in high strength applications. This series has less thread depth and a larger minor diameter than coarse series threads. Consequently, thinner walls are permitted for internal threads and more strength is available to external threads than for coarse series threads of the same nominal size.

8-Thread Series

The 8-thread series (8UN) is a uniform-pitch series for large diameters or as a compromise between coarse and fine thread series. Although originally intended for high-pressure-joint bolts and nuts, it is now widely used as a substitute for the coarse thread series for diameters larger than 1 inch.

12-Thread Series

The 12-thread series (12UN) is a uniform-pitch series for large diameters requiring threads of medium-fine pitch. Although originally intended for boiler practice, it is now used as a continuation of the fine thread series for diameters larger than 1-1/2 inch.