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Hex head cap screws and hex bolts. They look similar, and their names sound similar 鈥斅燽ut they鈥檙e different. How? Find out below.

What鈥檚 the Difference Between Hex Head Cap Screws and Hex Bolts? Definitions From ASME B18.2.1

It鈥檚 tricky to tell the difference between a hex head cap screw and a hex bolt. In fact, the topic falls squarely into the 鈥渄epends on who you ask鈥� 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 . It鈥檚 just one of the many specifications that address this subject, but it鈥檚 pretty common, thorough, and simple to understand.

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 录 – 1 陆鈥�, 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鈥檙e 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鈥檙e intended to be paired with a nut. They typically have diameters between 录 – 1鈥�, 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鈥檝e proposed some basic definitions of hex head cap screws and hex bolts, let鈥檚 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鈥檚 diameter must be perpendicular to the axis of the body with a tolerance of 3掳 for 1鈥� size and smaller, and 2掳 for greater than 1鈥�.

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 录鈥� nominal size hex head cap screw is 0.245鈥� and the maximum is 0.250鈥� 鈥斅燼 0.005鈥� difference.

Hex bolts have 鈥渓ooser鈥� tolerances and are a bit more lenient in this sense. For example, the minimum body diameter for a 录鈥� nominal size hex bolt is 0.237鈥� and the maximum is 0.260鈥� 鈥斅燼 0.023鈥� difference.

Material & Grade

Unless otherwise specified, hex head cap screws made of steel should comply with , , or . Hex head cap screws made of stainless steel should comply with .

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

Again, it鈥檚 important to remember that this is just one specification鈥檚 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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