Why do hex cap screws have dash marks on their heads?

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Home Improvement

Screws and bolts have different head shapes, types, and threading combinations. Among the head types, hex head or hex cap screws are unique because they require a special driver for installation and are used when extra torque is needed. However, if you look closely at the head of a hex cap screw, you will see lettering or dash marks that serve as a code to indicate the screw’s specifications. These markings indicate what standards the screw meets, what material it’s made of, and its load-bearing capacity.

For example, if a hex cap screw has three evenly spaced marks that start at the edge and point towards the center, it means it’s made of medium carbon steel that’s been quenched and tempered. Depending on its size, it has a minimum tensile strength of 90,000 to 120,000 pounds per square inch (psi). Meanwhile, hex cap screws with six dashes, each radiating from an angle towards the letters PB at the center, are Grade 8 screws made of medium carbon alloy steel. They have a minimum tensile strength of 150,000 psi.

To ensure consistency, manufacturers are required to include these markings on their products so that everyone in the industry has a common understanding. Manufacturers also include markings on their screws to indicate who the manufacturer was.

FAQ

1. What are the dash marks on hex cap screws?

The dash marks found on hex cap screws are used to indicate the grade of the screw. The number of dash marks corresponds to the screw’s strength, with more dashes indicating a higher grade.

2. How do I know which dash marks correspond to which grade?

The dash marks on hex cap screws are universally recognized and correspond to the following grades: one dash for grade 2, two dashes for grade 5, and three dashes for grade 8.

3. What is the difference between the grades?

The main difference between the grades of hex cap screws is their tensile strength. Grade 2 screws have a minimum tensile strength of 74,000 psi, grade 5 screws have a minimum tensile strength of 120,000 psi, and grade 8 screws have a minimum tensile strength of 150,000 psi.

4. When should I use a higher grade screw?

You should use a higher grade screw when you need a stronger connection. For example, grade 8 screws are commonly used in applications where a high level of strength is required, such as in heavy machinery or automotive applications.

5. Can I use a lower grade screw in place of a higher grade screw?

No, you should never use a lower grade screw in place of a higher grade screw. This can result in a weaker connection and can be dangerous in applications where a high level of strength is required.

6. Are there any other types of markings on hex cap screws?

Yes, there are other types of markings on hex cap screws that indicate the manufacturer, the material, and other information. These markings are typically found on the head of the screw.

7. Can I use a hex cap screw in place of a bolt?

Yes, a hex cap screw can be used in place of a bolt in many applications. However, it is important to ensure that the screw is the correct size and grade for the application.

8. Where can I purchase hex cap screws?

Hex cap screws can be purchased at hardware stores, home improvement stores, and online retailers. It is important to ensure that you are purchasing the correct size and grade of screw for your application.

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