We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is a Cap Screw?

By Dorothy Distefano
Updated May 17, 2024
Our promise to you
About Mechanics is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At About Mechanics, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

A cap screw is a type of fastener used for making mechanical connections between mating objects, to ensure that they are held together securely. These screws are commonly used to fasten machine parts and many other types of objects, such as those inside home appliances or consumer electronic devices. It is important to select the right size and type of cap screw for each individual application.

A cap screw is directly tightened into a threaded or tapped hole, and is normally used without a nut. It has a large head on one end and a cylindrical shaft with an external thread — a helical structure that allows the screw to be advanced when rotated. The tapped hole has an internal thread that matches the external thread of the screw. When this screw is inserted and rotated into a tapped hole, it advances. The screw is tightened and loosened by applying torque to the head of the screw using a tool.

A variety of cap screw heads are available to allow different tools to be used for tightening or loosening the screw. The head has a larger diameter than the threaded portion to provide a positive mechanical stop when tightening the screw, and to allow the head to be shaped to accept a specific type of tool. Examples of commonly used cap screw heads are the hex head, which has a hexagonal shape for use with a spanner wrench; the socket head, which has recessed hexagonal hole for use with an Allen wrench; and the button head, which has a lower profile, dome-shaped head and recessed hexagonal hole for use in counterbored holes.

A cap screw can generate a high amount of clamping force when tightened. The mating surfaces between the screw and nut resist the force being applied by the screw, and help to prevent the mechanical connection from loosening over time. The type and size of cap screw selected for a particular application depends primarily on the forces required to adequately secure the mechanical connection.

Cap screws are available in both English and metric sizes, and with a wide variety of coarse and fine threads. They can be manufactured using carbon steel, stainless steel, or brass for corrosion resistance; metal alloys for high-strength applications; and even plastic materials. When selecting a cap screw, it is important to understand the environment and stresses that the mechanical connections will be exposed to, so that the proper size and material are used.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By anon995675 — On May 19, 2016

A cap screw, by definition, is a machine bolt or screw that is threaded the to the cap and is normally fastened to a threaded hole rather than a nut. The picture of the "socket-head cap screw" accompanying this article would actually be a socket-head bolt, according to traditional definition.

By Izzy78 — On Aug 31, 2011

I needed to buy screws the other day, and I didn't realize how much variety there was. I was kind of overwhelmed.

I wasn't aware of the number system, or that might have been able to help me. Besides knowing the diameter you need (which was what I did know), you have a lot of options of the number of threads per inch, the size and shape of the head, and the screw material. Luckily I just needed some basic screws, so I wasn't too worried about making a perfect choice, but I'll definitely plan ahead next time.

By jcraig — On Aug 31, 2011

@JimmyT - The numbers on screws represent the gauge of the screw. The gauge refers to the diameter of the metal rod that was used to make the screw.

Oddly enough, the system used for screw gauges is the complete opposite compared to wire gauges. The larger a screw gauge gets, the larger the diameter of the screw becomes. With wire, smaller numbers are thicker, and larger numbers are thinner. I'm not sure where the conventions for these came about.

You can find reference charts online with the specifications for several screw types, but Number 5 screws are a quarter inch, and Number 14 screws are a half inch.

By JimmyT — On Aug 30, 2011

@jmc88 - I personally can't think of any other types of screws that wouldn't use this system.

The only thing I can think of is whether bolts are considered a type of screw. Since they are turned using a socket and need a nut to stay in place, they might fit, but it seems like bolts wouldn't really be considered a type of screw.

Out of curiosity, whenever I buy screws, they are always numbered depending on the size. I'm not talking about a length in inches, but a screw number. For example, the other day I needed screws so I went to the hardware store and bought a box of Number 5 screws. Where does that number come from?

By jmc88 — On Aug 29, 2011

So from what I understand, a cap screw is just another name for a regular, everyday screw. Is that right? I've never heard it called that, but I guess the term cap could refer to the fact that this is a head on the screw that can be turned with a screwdriver.

I suppose that begs the question of what are the names of some of the other types of screws? The article mentions that cap screws do not usually have a nut on them. Is there a name for screws that usually do need a nut?

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.