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Hex Bolt vs. Cap Screw: What’s the Difference?

by: Blue Ribbon Fastener | July 06, 2026
 

Time to Read: 6m 39s

The terms hex bolt and hex cap screw are often used interchangeably, but they are not always the same fastener. While both feature a six-sided hexagonal head and are used in a wide range of industrial and construction applications, there are important differences in how they are manufactured, installed, and specified.

Understanding these distinctions can help engineers, contractors, maintenance professionals, and purchasing teams select the right fastener for the job.

Hex bolt vs. cap screw at a glance

Hex bolt

A threaded fastener with a six-sided head, typically designed to pass through unthreaded holes and be secured with a nut.

Common uses:

  • Structural steel
  • Construction
  • Heavy equipment
  • Infrastructure projects
  • Industrial maintenance

Hex cap screw

A six-sided fastener manufactured to tighter dimensional tolerances (ASME B18.2.1), typically designed to thread directly into a tapped hole.

Common uses:

  • Machinery and equipment
  • Pumps and motors
  • Precision assemblies
  • OEM equipment
  • Automation equipment
Browse hex bolts → Browse hex cap screws →

Key differences

Feature Hex bolt Hex cap screw
Typical installation Used with a nut Threads into a tapped hole or may be used with a nut
Manufacturing tolerances Standard Tighter dimensional tolerances (ASME B18.2.1)
Threading Often partially threaded Available in partial and full thread configurations
Washer face May not include a washer face Typically includes a washer face under the head
Typical applications Structural and general construction Machinery and precision equipment
Although these distinctions exist, many distributors and manufacturers use the terms interchangeably — especially in general industrial applications. When precision or code compliance matters, always verify the specification required.

Threading differences

Thread length is one of the more practical differences between these two fasteners.

Many hex bolts feature a partially threaded shank, where the unthreaded grip section helps resist shear forces — particularly useful in structural and construction applications. Hex cap screws are available in both partially threaded and fully threaded versions depending on the assembly requirement.

When replacing an existing fastener, always verify the required thread length before ordering. Substituting a fully threaded fastener in a shear application can affect performance.

When to use each fastener

Choose a hex bolt when…

  • Joining multiple materials with through holes
  • Installing structural steel
  • Fastening heavy equipment
  • Using a nut and washer assembly

Commonly paired with: hex nuts, heavy hex nuts, flat washers, lock washers

Choose a hex cap screw when…

  • The assembly includes a tapped hole
  • Space is limited
  • Precise fit is required
  • Equipment manufacturers specify cap screws

Frequently found in OEM equipment and machinery where consistent tolerances are critical

Browse nuts →

Materials and finishes

Both hex bolts and cap screws are available in a variety of materials and finishes. The right choice depends on the application environment, corrosion requirements, and strength specifications.

Option Materials Finishes
Available in Carbon steel, alloy steel, stainless steel Zinc plated, hot-dip galvanized, black oxide, plain
Browse stainless steel fasteners →

Strength grades

Strength is determined by grade and material — not by whether the fastener is called a bolt or a cap screw. Always verify project specifications before selecting or substituting a fastener.

System Common grades Standard
Imperial Grade 2, Grade 5, Grade 8 SAE J429
Structural A325, A490 ASTM F3125
Metric Class 8.8, Class 10.9, Class 12.9 ISO 898-1

Common applications

Hex bolts

  • Structural steel connections
  • Construction equipment
  • Bridges
  • Utility infrastructure
  • Agricultural equipment
  • General industrial assemblies

Hex cap screws

  • Manufacturing equipment
  • Pumps and compressors
  • Electric motors
  • Machine frames
  • Automation equipment
  • OEM assemblies

Frequently asked questions

Is a hex bolt the same as a hex cap screw?
Not exactly. While the terms are often used interchangeably, hex cap screws are typically manufactured to tighter tolerances (ASME B18.2.1) and include a washer face under the head. Hex bolts are generally intended for use with nuts in through-hole applications.
Can a cap screw be used with a nut?
Yes. Although cap screws are often threaded into tapped holes, they can also be used with nuts when the application requires it.
Are hex bolts fully threaded?
Not always. Many standard hex bolts are partially threaded, with an unthreaded grip section that helps resist shear forces in structural applications. Thread length varies by size and specification.
Which fastener is stronger?
Strength depends on the material and grade — not whether the fastener is called a bolt or a cap screw. Grade 8, A325, and A490 all have different strength characteristics. Always verify the required grade for your application.
How do I know which fastener my application requires?
Review engineering drawings, equipment documentation, or project specifications. If you’re replacing an existing fastener, match the thread size, grade, material, finish, and thread length exactly.

Need help selecting the right fastener?

Choosing between a hex bolt and a hex cap screw depends on how the fastener will be installed, the required strength, and the demands of the application.

Blue Ribbon Fastener supplies hex bolts, hex cap screws, structural fasteners, machine fasteners, and industrial hardware for construction, manufacturing, OEM, and maintenance applications.

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