Explore the Different Types of Hex Head Screws

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The screw has evolved since ancient times to be one of our most used and versatile tools. What may have been designed as a method of removing water from a well has since developed into our most useful fastener.

Moving Beyond Square-head Screws

In the 18th and 19th centuries, the square-head screw was the most inexpensive screw to mass produce, so it was commonly used until the beginning of the Industrial Revolution. During the Industrial Revolution and the innovations in mass production it spawned, engineers realized that the square-head screw was actually slowing down production because of the limited number of angles that could be used to access it. This slowdown cost money, and the hexagonal heads screw, with its greater number of faces, proved to be the most efficient and cost-effective screw to use quickly.

The discovery that the hexagon shape was the most efficient shape to be used for grabbing onto and tightening these screw fasteners resulted in the development of many different varieties of hex head screw types and socket cap screws.

What are Hex Head Screws?

Hex head screws, also known as hex bolts, are a type of fastener that features a hexagonal head designed to be tightened or loosened with a wrench or socket tool. They come in various sizes and materials, and they have different variations to suit specific applications.

These are not to be confused with socket head cap screws. Socket head cap screws are one of the most popular variations. These screws do away with the hexagonal shape of the head and employ an interior hexagonal-shaped hole in the cap that accepts an Allen-type wrench as a driver. They are much more suited for applications in tight quarters, as they can be accessed from the top and don&#;t demand the elbow room to turn a wrench that the hex head bolt does.

These newer types of screws take their place among the various other types of screws that have established a place in modern mechanics. The variations include:

Hex Cap Screw. This is the standard hex head screw. It's used in a wide range of applications where a secure fastener applied with a wrench or socket is required.

Hex Socket Head Cap Screws. These popular screws have a cylindrical head and an internal hex socket drive. They are commonly used in applications where a low-profile, flush installation is desired.

Hex Tap Bolt. Similar to a hex cap screw. These bolts are often used in construction and industrial applications where a non-removable fastener is needed.

Hex Flange Bolt. This bolt has an integral flange that serves as a built-in washer. It's often used in automotive and structural applications, where the flange distributes the load and eliminates the need for a separate washer.

Hex Serrated Flange Bolt. Similar to a hex flange bolt, this type has serrations under the flange to help prevent loosening due to vibrations. It's commonly used in machinery and equipment assembly.

Hex Machine Screws. These smaller-sized hex screws are used in applications that require threaded fasteners but in smaller sizes, such as electronics, machinery, and appliances.

Hex Lag Screws. Also known as a lag bolt, it has a larger body and is designed to be used with a nut and washer. These screws are commonly used for fastening wood to wood or wood to metal in construction and woodworking.

Hex Head Set Screws. These screws have no head and are fully threaded. They are used to secure one object within or against another, often used in conjunction with a threaded hole.

These variations of hex head screw types cater to a wide range of applications, including construction, automotive, machinery, electronics, and woodworking. The right choice of hex head screw depends on factors such as load requirements, material compatibility, aesthetics, and the specific function within the assembly.

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Hex head cap screws and hex bolts. They look similar, and their names sound similar &#; but they&#;re different. How? Find out below.

What&#;s the Difference Between Hex Head Cap Screws and Hex Bolts? Definitions From ASME B18.2.1

It&#;s tricky to tell the difference between a hex head cap screw and a hex bolt. In fact, the topic falls squarely into the &#;depends on who you ask&#; category, right alongside the differences between generic bolts and screws.

However, there are a few manufacturers and industry organizations that have provided their expert opinion here. One explanation we like best is from The American Society of Mechanical Engineers (ASME) B18.2.1 standard. It&#;s just one of the many specifications that address this subject, but it&#;s pretty common, thorough, and simple to understand.

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What Are Hex Head Cap Screws?

According to ASME B18.2.1, screws are externally threaded fasteners capable of being inserted into holes in assembled parts, mating with preformed internal threads, forming their own internal threads, and being tightened or released by torquing their heads.

Hex head cap screws are a particular type of screw with a hexagon-shaped head designed to be inserted into a pre-tapped hole. They typically have diameters between ¼ &#; 1 ½&#;, can be partially or fully threaded, and are available in a variety of grades.

Hex head cap screws are most commonly used in automotive and heavy machinery applications.

What Are Hex Bolts?

According to ASME B18.2.1, bolts are externally threaded fasteners designed for insertion through holes in assembled parts. They&#;re usually meant to be tightened or released by torquing a nut.

Hex bolts are a particular type of bolt with a hexagon-shaped cap on one end. They&#;re intended to be paired with a nut. They typically have diameters between ¼ &#; 1&#;, can be partially or fully threaded, and are available in a variety of grades.

Hex bolts are most commonly used in construction and heavy machinery applications.

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Physical Differences Between Hex Head Cap Screws and Hex Bolts, According to ASME B18.2.1

Now that we&#;ve proposed some basic definitions of hex head cap screws and hex bolts, let&#;s take a look at some of the more prominent differences in their physical features and performance.

Washer Face

Hex head cap screws have a washer face under their heads.

Hex bolts do not have a washer face.

Bearing Surface

In this spec, hex head cap screws have a maximum measurement of total bearing surface runout, which varies based on nominal size and diameter.

For hex bolts, this spec only dictates that a hex bolt&#;s diameter must be perpendicular to the axis of the body with a tolerance of 3° for 1&#; size and smaller, and 2° for greater than 1&#;.

Tolerance & Body Diameter

In general, hex head cap screws are a little more refined and precise than hex bolts. They have tighter tolerances across the board, no matter the size of the part. For example, the minimum body diameter for a ¼&#; nominal size hex head cap screw is 0.245&#; and the maximum is 0.250&#; &#; a 0.005&#; difference.

Hex bolts have &#;looser&#; tolerances and are a bit more lenient in this sense. For example, the minimum body diameter for a ¼&#; nominal size hex bolt is 0.237&#; and the maximum is 0.260&#; &#; a 0.023&#; difference.

Material & Grade

Unless otherwise specified, hex head cap screws made of steel should comply with ASTM A449, ASTM A354, or SAE J429. Hex head cap screws made of stainless steel should comply with ASTM F593.

Hex bolts made of steel should comply with ASTM A307 Grade A unless otherwise specified. For more information on different bolt grades and their applications, check out this blog.

Again, it&#;s important to remember that this is just one specification&#;s definition of the difference between hex head cap screws and hex bolts. Depending on what spec you look at, you may be presented with a different answer to this question.

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Need hex head cap screws or hex bolts? At Wilson-Garner, we can manufacture both according to your specifications. Our team specializes in per-spec, limited-run fastener solutions for a range of industrial applications. Contact us online to learn more about how we can help you.

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