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Cap Screws versus Bolts — There Is A Difference

Learn the difference: Cap Screw Versus Bolts — When to use each

If you’ve ever wondered why different names refer to two similar-looking bolts, you’ve come to the right place. In this article, I’ll explain the differences between a cap screw versus bolts and where each is used. Understanding them can help you choose the right fastener for the job.

What’s the Key Difference: Cap screw versus bolt

The main difference lies in how each fastener is designed to be used:

• Hex Bolt Usage— Hex bolts are designed to work with a hex nut. You insert the bolt through a hole, thread on the nut, and tighten the nut, not the hex head, to secure the connection. They’re common in construction and heavy machinery, where strength and simplicity are key.

• Hex Cap Screws Usage— Hex Cap Scrwes, on the other hand, are designed to thread directly into a tapped (pre-threaded) hole. You tighten them by turning their head, and they’re often used in precise applications like machinery or automotive assembly.

Physical Features That Set Them Apart

Washer Face
Cap screws have a built-in washer face under their head. This provides a smooth, even surface for tightening and helps distribute the load more evenly. Hex Bolts don’t have this feature.

Threading and Ends
Cap screws typically have a chamfered (slightly angled) end for easier threading into pre-tapped holes. Bolts usually have flat ends since they rely on a nut to create the connection.

Tolerances
Cap screws are manufactured to tighter tolerances than bolts. This precision makes them ideal for applications where exact fit and alignment are critical. For example, the diameter of a cap screw might vary by just 0.005 inches, while a bolt of the same size could have a larger tolerance range.

This image shows the differences between a cap screw versus a bolt

Cap screw vesus bolt

How They’re Made

The manufacturing process also differs slightly

Hex Bolts are usually hot-forged, which is a more straightforward process that is ideal for producing durable fasteners quickly.

Cap Screws are often made using a cold-heading process or precision machining, resulting in finer threads and tighter tolerances.

Where You’ll See Them Used

Cap Screws versus Bolts

Hex bolts— These are your go-to for heavy-duty applications like construction, structural steel connections, or securing through-hole parts in heavy machinery. They’re all about strength and reliability. Primarily designed to be used with a nut.

Hex Cap Screws— These are more refined, making them ideal for automotive work, machinery assembly, or any situation where precise fit and load distribution matter. Designed to be threaded into pre-made threads.

Common Bolt Materials and Grades

Fasteners are made in various materials and grades depending on the application:

Hex Bolts
Grade A307: General-purpose, low-carbon steel bolts used in construction.
Grade A325: High-strength structural bolts for steel-to-steel connections.
Grade B7: Heat-treated alloy steel bolts for high-temperature or high-pressure applications.

Hex Cap Screws
Grade 5: Medium-strength fasteners made from heat-treated carbon steel and often used in automotive and construction industries. The tensile strength for Grade 5 cap screws is 120,000 psi (diameters 1/4″ – 3/4″).
Grade 8: High-strength alloy steel screws for demanding applications. The tensile strength for Grade 8 cap screws is 150,000 psi (diameters 1/4″ – 1-1/2″).
304 Stainless Steel: Known for corrosion resistance, used in marine, food processing, and chemical environments.
316 Stainless Steel: Even more corrosion-resistant due to its molybdenum content. Perfect for harsh environments like saltwater or industrial chemicals.

Cap screws versus bolts: How to Tell Them Apart in a Nutshell

If you’re trying to decide between a hex bolt and a hex cap screw, ask yourself these two questions:

• Does the fastener need to work with a nut? If yes, go with a bolt.

• Is precision or load distribution critical? If yes, a cap screw is the better choice.

Understanding the difference between a cap screw versus bolt isn’t just a matter of semantics—it’s about using the right tool for the job. Whether you’re building a deck, assembling a machine, or working on your car, choosing the right fastener ensures safety, performance, and longevity.

©, 2025 Rick Muscoplat

Posted on by Rick Muscoplat



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