Glossary
Common Stainless Steel Fastener Terms, Descriptions & Reference Materials
This glossary is provided as a reference only. For additional information please contact our sales department.
Austenitic - Refers to 300 series stainless steel, the most popular of all the stainless steel alloys. This accounts for 85%-90% of stainless steel fasteners sold. Austenitic stainless is a crystal structure formed by the heating of steel, chromium, and nickel to form the characteristics of 300 series stainless steel. Austenitic fasteners have the highest level of corrosion resistance in the stainless steel family. They cannot be hardened by heat-treating, and are non-magnetic for practical purposes. The most common types are generically known as “18-8 Stainless” and include the grades of 302, 302HQ, 303, 304 and 305.
AN - Stands for Air Force-Navy.
Bolt versus Screw - These 2 terms are used interchangeably as there is really no difference between the two fasteners.
Cold Forming, Cold Heading, or Cold Working - When fasteners are produced with little or no heat. Work is done by pressing metal wire against various dies at high speeds to form the fastener's head or basic shape. Cold working causes an increase in tensile strength and hardness.
18-8 - refers to 300 series stainless steel having approximately (not exactly) 18% Chromium and 8% Nickel. The term “18-8” is used interchangeably to describe 302, 302HQ, 303, 304, & 305 stainless steel. There are little overall differences in corrosion resistance among the 18-8 types, but slight differences in chemical composition do make certain grades more resistant to particular chemicals and atmospheres. 18-8 has superior corrosion resistance and are generally non-magnetic.
Galling (AKA: Seizing)- When to fasteners sticks together and cannot be easily loosened. In tightening fasteners, pressure builds on threads as metals rub together, and the passive film preventing corrosion may not form due to lack of oxygen.
Hot Forging - Heating metal to red hot temperatures or temperatures above the recrystallization point to soften it before shaping. Hot forming is generally used when the diameter of the fastener is too large for the cold heading process or the quantities required is low.
Magnetism - As it relates to stainless steel, 300 series stainless steel is non-magnetic in its raw material condition. Cold working can sometimes induce traces of magnetism, depending on the amount of work and chemical composition of the stainless steel. A rise in magnetism related to an increase in tensile strength and work hardening caused by the heat and friction of cold forming and doesn't reduce the corrosion resistance of the fastener.
Non-Ferrous - Metals without iron. Brass and Silicon Bronze are non-ferrous: stainless steel is often categorized as non-ferrous, but is not.
Passivating - for this purpose it means to clean. The purpose of passivating is to remove both grease and traces of particles left from the manufacturing process. A wide range of cleaning methods are used containing nitric, phosphoric and other acids. For fasteners that have been properly cleaned, the method is used is impossible to determine.
Passive Film - The major characteristic of stainless steel is its ability to form a thin layer of protection called a “Passive Film”; on it's outer surfaces. This film results from a continual process of low-level oxidation. Once formed, it prevents further oxidation or corrosion from occurring.
Pitch - The distance between two adjacent threads measured at the outside diameter of the threads.
Roll threads - Forming threads on a fastener by pushing or rolling dies against the fastener without the any removal of material. Roll threading hardens the material begin worked, making the threads stronger.
SAE - Stands for “Society of Automotive Engineers”.
Silicon Bronze - An alloy made up of 95-98% Copper plus a small amount of silicon added for strength. The material is highly resistance to seawater corrosion.
Stainless Steel - With the addition of 12% chromium to iron, stainless steel is formed. The chromium protects the iron against most corrosion or red-colored rust. The ability of the fastener to create a passive film is the most important part in stopping corrosion. The overriding purpose of stainless steel is to provide corrosion resistance against A) Atmospheric conditions B) Chemicals C) Extremes in Weather D) Changing environments.
Threads - Class 2 threads compose 90% of the stainless fasteners and have normal commercial tolerances. About 90-95% of all the stainless steel fasteners are coarse thread.
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