Hex cap screws are commonly used in construction and industrial fastening applications. Like all screws, they feature a threaded shank. While other screws typically have a drive recess in the head, though, hex cap screws feature a solid head that shaped like a hexagon. This hexagonally shaped head allows them to be driven into objects with a wrench.
When choosing hex cap screws, you need to consider the grade. There are many different grades in which they are available, some of which are stronger than others. What are hex cap screw grades exactly, and why are they important?
Overview of Hex Cap Screw Grades
The grade of a hex cap screw indicates the fastener’s strength and physical properties. Contrary to what some people believe, grades have nothing to do with size. To determine the size of a hex cap screw, you should refer to its length and diameter. The grade simply reveals how strong a given hex cap screw is — and you can use this information to determine if it’s appropriate for a particular application.
Grade 2 Hex Cap Screws
There are grade 2 hex cap screws. They are typically made of low- or medium-carbon steel and designed for low-stress applications. Grade 2 hex cap screws are among the most basic type. They are inexpensive and readily available, but they lack the strength of their higher-grade counterparts.
Grade 5 Hex Cap Screws
Grade 5 hex cap screws are slightly stronger. They are typically made of heat-treated, medium-carbon steel, boasting a tensile strength of about 120,000 PSI. While grade 2 hex cap screws are often unmarked, grade 5 hex cap screws may feature three radial lines on the head.
Grade 8 Hex Cap Screws
There are also grade 8 hex cap screws. They are typically made of heat-treated alloy steel and offer a tensile strength of about 150,000 PSI. With their high tensile strength, grade 8 hex cap screws are commonly used in suspension systems, industrial equipment and other applications involving high loads. You can identify them by looking for six radial lines printed on the head.
Metric Grades
Grades 2, 5 and 8 are all standard U.S. grades for hex cap screws. However, you can also find hex cap screws in metric grades. Common metric grades include 8.8, 10.9 and 12.9.
Grade 8.8 hex cap screws are made of medium-carbon, heat-treated steel. They offer the equivalent strength of grade 5 hex cap screws.
Grade 10.9 hex cap screws are made of medium-carbon, heat-treated alloy steel. They have a higher tensile strength than grade 8.8, boasting a similar strength as grade 8 hex cap screws.
Finally, grade 12.9 hex cap screws are among the strongest on the market. They are made of high-strength alloy steel and boast a tensile strength of about 180,000 PSI. Given their superior strength, they tend to cost more than other, lower grades of hex cap screws.