Difference Between Hex Head Cap Screws and Hex Bolts

Distinguishing hex head cap screws and hex bolts can be perplexing, often landing in the realm of “it varies depending on whom you consult.” This topic sits snugly in a domain where opinions diverge, much like the ongoing debate over the nuances between general bolts and screws.

However, a particularly clear-cut explanation comes from The American Society of Mechanical Engineers (ASME) B18.2.1 standard. This standard, amidst a sea of specifications addressing this issue, stands out for its widespread acceptance, comprehensive coverage, and clarity.

What are Hex Head Cap Screws

Per ASME B18.2.1, screws are externally threaded fasteners designed for insertion into holes in assembled parts. They can mate with preformed internal threads, form their own internal threads, and are tightened or released by torquing their heads.

Hex head cap screws are a specific type of screw with a hexagonal head, intended for insertion into a pre-tapped hole. Typically, they range in diameter from ¼ – 1 ½ inches and can be partially or fully threaded. They come in various grades and are often employed in automotive and heavy machinery applications.

What are Hex Bolts

Hex bolts, as outlined by ASME B18.2.1, are externally threaded fasteners purposed for passage through holes in assembled parts. They are generally fastened or loosened by torquing a nut.

These bolts feature a hexagonal cap and are designed to be used in conjunction with a nut. Hex bolts typically range in diameter from ¼ – 1 inch, and like their cap screw counterparts, can be partially or fully threaded and available in multiple grades.

Hex bolts find their common use in construction and heavy machinery applications.

Comparing Physical Features: Hex Head Cap Screws vs. Hex Bolts

Now, let’s focus on some key physical differences between these two, as per ASME B18.2.1:

  • Washer Face: Hex head cap screws possess a washer face under their heads, while hex bolts do not.
  • Bearing Surface: The spec for hex head cap screws includes a maximum total bearing surface runout, varying based on size and diameter. For hex bolts, the spec requires the bolt’s diameter to be perpendicular to the body axis, with a tolerance of 3° for sizes 1” and smaller, and 2° for sizes over 1”.
  • Tolerance & Body Diameter: Hex head cap screws generally have tighter tolerances, exemplified by a minimum body diameter of 0.245” and a maximum of 0.250” for a ¼” nominal size. Hex bolts, conversely, have more relaxed tolerances, with a minimum body diameter of 0.237” and a maximum of 0.260” for the same nominal size.
  • Material & Grade: Unless specified otherwise,steel hex head cap screws should adhere to ASTM A449, ASTM A354, or SAE J429 standards, while stainless steel varieties should comply with ASTM F593. Hex bolts made of steel are typically expected to meet ASTM A307 Grade A standards, unless otherwise specified.

It’s crucial to remember that this is just one perspective on the differences between hex head cap screws and hex bolts, and different specifications might offer varying interpretations.

Sourcing Hex Bolts from Gulian

If you’re in need of hex bolts, Gulian can provide both, tailored to your specifications. Specializing in per-spec, limited-run fastener solutions for various industrial applications, their team can assist you in finding the right fastener for your needs. To learn more about their offerings, reach out to them online.

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