Trying to determine the right fastener for your application, but getting lost in all the jargon and technical specifications that are out there? Trust us, you’re not the only one.
The fastener industry can be complicated, especially if you need a part that’s more specialized than your typical Phillips-head screw. There are a ton of new, technical terms to learn — but we’ve got you covered. Here’s a glossary-style list with some of the most important fastener terms and abbreviations you need to know.
A Guide to Fastener Terminology
Below is a list of about 50 different fastener terms and abbreviations, which are categorized into five different sections: types, manufacturing processes, measurement, testing, and standards and specifications.
While this is by no means a complete list of all the fastener terminology out there, it’s a good starting point for some of the most common terms to know going into your project.
If you have a question about a term or concept that isn’t defined on this list, don’t hesitate to reach out to us! We’re happy to help. Also, be sure to browse the links associated with some of these terms, as they’ll lead you to our articles with more information regarding each subject.
Bolt – An externally threaded fastener designed for insertion through holes in assembled parts. It’s normally intended to be tightened or released by torquing a nut.
Countersunk – Used to describe a fastener head that rests evenly with or below the material surface after installation. The design tapers toward the fastener shank, allowing the head to essentially “sink” into the surface.
Carriage bolt – A type of bolt with a threaded bar and a domed, enlarged head on one end that’s designed to keep the bolt from pulling through.
External drive – A fastener head that requires a tool, like a wrench, to wrap around the head for installation and removal.
External thread – Threading on the outside of a cylindrical fastener.
Head style – The type of head or top on a fastener, such as a round or hex head style.
Hex head – A fastener head with six vertical sides and a flat bearing surface.
Hex flange head – A fastener head with six vertical sides that expand out to a flat, washer-like bearing surface at the bottom.
Internal drive – A fastener head that requires a tool, like a screwdriver, to be inserted within the head for installation and removal.
Internal thread – Threading on the inside of a cylindrical, holed fastener.
MS fastener – Abbreviation for “mil-spec” or “military specification.” It’s a type of fastener that’s designed and maintained by the United States Military.
Non-countersunk – Used to describe a fastener head that protrudes from the material surface after installation, leaving the head fully exposed. The design includes a narrow shank that’s topped with an abrupt, wide head.
Place bolt – A self-locking, free-spinning hex head bolt that prevents loosening due to vibration. It offers up to seven times more vibration resistance than a conventional hex head cap screw.
Screw – An externally threaded fastener designed for insertion through holes in assembled parts, mating with a preformed internal thread, or forming their own thread. It’s tightened and released by torquing a head.
Specialty fastener – A fastener that’s designed and manufactured for a certain industry, application, or material. It’s made with unique specifications that set it apart from common fasteners you’d find at a hardware store or use in a widely practiced application.
Stud – An externally threaded fastener that typically looks like and operates as a threaded bar. It’s commonly used to join two components with internally threaded holes together
Washer – A thin plate with a hole in the middle, which is used to distribute the load and increase the bearing surface of a threaded fastener.
Fastener Manufacturing Processes
Cold forming – Also known as cold heading, this is a process of forming a fastener without heating up the material. It’s usually accomplished by striking or pressing the material within a form, or die, to create a part with desired specifications.
Fastener coating – A chemical that’s applied to the exterior of a fastener to improve its performance and longevity (e.g. zinc phosphate, cadmium electroplate, etc.)
Short-run production – Also known as limited-run production, this is a process in which a manufacturer accepts and fulfills orders involving relatively small quantities of product. At Wilson-Garner, we use short-run production to manufacture specialty fasteners in smaller quantities.
Thread cutting – The process of producing external threads on a fastener by cutting away, or removing, material from a round bar.
Thread rolling – The process of producing external threads on a fastener by rolling it through a set of threading dies that displace the material to form threads, without removing any material or changing its grain structure.
Body diameter – The diameter of the body (or smooth part) of the fastener, which is generally located above the threads.
Major diameter – The largest diameter of a fastener thread. It’s measured from the crest (top) of a thread on one side to the crest of a thread on the other side.
Minor diameter – The smallest diameter of a fastener thread. It’s measured from the root (bottom) of a thread on one side to the root of a thread on the other side.
Nominal diameter – This is shorthand for “nominal major diameter” — and, in most cases, “nominal” just means “basically.” So it’s an estimated major diameter.
Pitch – The distance from a point along one thread to that same point on the next thread. You can measure pitch from the crest, the trough, or any point in between.
Pitch diameter – The diameter of a theoretical cylinder that exists halfway between the major and minor diameters.
TPI – Abbreviation for threads per inch. As the name suggests, it’s calculated by counting the number of thread peaks along a 1-inch length.
UNC – Abbreviation for Unified National Coarse thread. It’s the United States’ standard for fasteners with coarse threads. Coarse threads are bigger, and there are therefore fewer of them on a fastener.
UNF – Abbreviation for Unified National Fine thread. It’s the United States’ standard for fasteners with fine threads. Fine threads are smaller, and there are therefore more of them on a fastener.
Bearing surface testing – Fastener testing method that measures how much the amount of surface area and roughness of the bottom of the fastener head or washer will affect friction.
Coefficient of friction – Fastener testing method that measures the kinetic and static resistance of the surfaces of a bolted joint as it’s being tightened.
Hardenability testing – The testing of a material that provides data on the changes in hardness of a material as it’s heated to various temperatures.
NSS testing – Abbreviation for neutral salt spray testing. It’s a fastener testing method that measures corrosion resistance by inserting it in a test chamber with salt spray for a specified number of hours.
Proof load – The minimum amount of force a fastener must be able to withstand for a given amount of time without experiencing permanent deformation.
Tensile strength – The maximum force that a fastener can withstand before fracturing.
Torque-tension testing – Fastener testing method that measures the input torque required for a bolted joint to achieve a specified tension.
Yield strength – The load that’s carried at the point where a fastener experiences permanent deformation.
Fastener Standards and Specifications
ASME – Abbreviation for The American Society of Mechanical Engineers. It’s an organization that creates quality standards for five main industries: bioengineering, robotics, clean energy, manufacturing, and pressure technology.
ASTM – Abbreviation for The American Society for Testing and Materials. It’s an organization that created one of the first quality standards sets, and it now focuses on six types of standards related to the manufacturing process: test method, specification, classification, practice, and guide and terminology.
DIN – Abbreviation for Deutsches Institut für Normung, or the German Institute for Standardization. It’s an organization that creates quality standards, but many of those standards have been outright replaced by ISO standards.
IATF – Abbreviation for The International Automotive Task Force. It’s an organization of automotive manufacturers and their trade associations — all of who work to provide consistent quality management standards for automotive suppliers worldwide.
ISO – Abbreviations for The International Standards Organization. It’s an organization that establishes widely used standards for a multitude of manufacturing applications. It’s by far the most common standard for establishing an overreaching quality management system (QMS).
Grade – A set of characteristics, defined by a standard, that determines the material, hardness, and strength of a fastener. Many standards require distinct head markings to make the grades easier to identify.
Property class – The metric equivalent to the standard (or inch) term “grade.”
QMS – Abbreviation for quality management system. It outlines all the policies and procedures put in place by a company to ensure that its products and services meet customer requirements.
SAE – Abbreviation for The Society of Automotive Engineers. It’s a United States-based organization that’s composed of automotive and aerospace engineers, and that creates its own quality standards for manufacturing applications.
Have More Questions on Fastener Terminology? Contact Us.
The fastener industry can get a bit technical and confusing — but by working with Wilson-Garner, it doesn’t have to be. Our specialty fastener experts are here to help you decipher the details and find the right solution for your application. Contact us to learn more about our products, processes, and how we can best support you.