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Hex Bolts vs. Hex Cap Screws

Knowing the Difference

Hex cap screws and hex bolts are two of the most commonly used fasteners in industrial and construction applications. While these fasteners are often used interchangeably, there are key differences in their design, specifications, manufacturing standards, and recommended applications. Understanding these differences will help you choose the right fastener for your specific job.

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Hex Cap Screws

Hex cap screws are precision fasteners featuring a hexagonal head and either a partially or fully threaded shank. They're typically used in pre-tapped holes and are manufactured to tighter tolerances than standard bolts.

Key Characteristics:

  • Precision-machined threads

  • Typically includes a washer face under the head

  • Usually manufactured by a cold-heading process or turned CNC operation

  • Conform to tighter manufacturing standards, often ASME B18.2.1

  • Other common fastener specifications includes: ASTM A449 and SAE J429 Grade 2, 5, and 8

  • Designed to be tightened by turning the head of the cap screw

Hex Bolts

Hex bolts, also known as hex head bolts, have a similar hexagonal head but are generally manufactured to looser tolerances. Most hex bolts do not have a washer face and are commonly used with a nut or in applications where the bolt passes through unthreaded material.

Key Features:

  • Looser manufacturing tolerances

  • Typically no washer face under the head

  • Designed to have a nut tightened onto the bolt

  • Suitable for general-purpose fastening

  • Other common fastener specifications include: ASTM A307, A354, and F1554

In most cases, the choice between a hex bolt and a hex cap screw isn't one you'll actively make. The decision is typically driven by factors such as material grade, thread specifications, and commercial availability. Fortunately, for the vast majority of applications, hex bolts and hex cap screws can be used interchangeably without any functional difference. While there are technical distinctions between the two—such as differences in manufacturing tolerances and threading—their performance in standard fastening applications is largely equivalent.

Attributes of Bolts and Cap Screws

Under-Head Radii and Body Diameter

The under-head radii and body (or "shank") diameters. The hex bolt; has a higher maximum tolerance on its under-head radius and body diameter than the cap screw which potentially makes its under-head juncture much sturdier and resistant to fracturing and failures. However, the lower side of its tolerances are below that of a typical cap screw. Which could provide varying results in performance.

Though similar, only the hex cap screw can be interchanged with most comparable assemblies using a hex bolt. Unfortunately, the same cannot be said for the hex bolt, as its larger tolerance zones could easily compromise the integrity of assemblies that primarily utilize hex cap screws.

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Stainless Steel Grade Markings

Stainless Steel Grade Markings

Tensile Strength

Tensile strength

Steel Grade Markings

Steel grade markings