Key Takeaways
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A hex cap screw has tighter tolerances and a chamfered end with a washer face under the head. A hex bolt has a flat end and no washer face. In most cases, there is no operational difference between them.
To the naked eye, there does not appear to be much difference between a bolt and a screw. Both are threaded fixings with a head for tightening, but there is more to it than that. The first time a customer asked for a whiz nut, it was not immediately clear which part they meant, and that is exactly the point of this guide.
Hex Cap Screw Hex Bolt
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Fastener slang varies by industry, region, and trade. The same part can have multiple informal names.
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Royal Brass and Hose has stocked fasteners since acquiring Cornette Fasteners in the late 1980s and currently carries over 16,000 types.
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When in doubt, contact a Royal Brass and Hose sales representative to match a slang term to the correct official part name.
Hex Cap Screw vs. Hex Bolt
A hex cap screw has tighter tolerances on the body dimensions and features a chamfered end and a washer face under the bolt head. A hex cap screw is often called a finished hex bolt. Hex bolts have a flat end and lack the washer face under the head.
Fastener Slang Reference Table
The table below maps 25 common fastener slang terms to their official Royal Brass and Hose part names, with links to shop where available.
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Slang Term |
RBH Part Name |
Definition |
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1/2 Nut |
A thinner pattern of nut, sometimes used as a second nut to 'jam' another nut in place to prevent loosening. |
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1/2 Moon Key |
Used to connect a rotating machine element to a shaft. Prevents relative rotation between the two parts and enables torque transmission. |
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Allen Head Bolt |
Refers to a hex head cap screw: a hex bolt with a circular washer face under the head. In most cases there is no operational difference between a hex head cap screw and a hex bolt. Hex caps should not be confused with socket caps. |
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Allen Wrench / Hex Key |
N/A |
A hex key or Allen key is a simple tool used to drive bolts and screws with hexagonal sockets in their heads. |
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Automation Nut / Stover Lock Nut / Top Lock Nut |
All-metal lock nuts are used in cases where nylon insert lock nuts are not practical, such as in high-heat applications. |
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Bolt |
Bolts with a hexagon-shaped head and machine threads for use with a nut or in a tapped hole. |
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Butterfly Nut |
A nut with wings for easy manual assembly. |
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Cap Nut |
A nut with a slightly pointed domed top that covers the end of a bolt. Acorn nuts are sometimes confused with cap nuts, which are domed but lack a point. |
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Case Locking Bolts |
Serrated Screw |
Screws with a flange at least 10% larger than a standard flange for more gripping power. Serrations under the head grip the material surface for mild vibration resistance. |
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Castle Nut |
Slotted nuts have grooved heads that align with holes in the mated bolt to accept a cotter pin, locking the nut in place. |
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Connector Nut / Rod Coupling Nut |
N/A |
Coupling nuts are internally threaded fasteners that join threaded rods, pipes, and other threaded parts, sometimes of differing sizes. |
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Countersunk Bolt / Flat Head |
N/A |
Used when a smooth surface is required. Common applications include bridge decking, walkways, and railing. |
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ESNA Nut |
A locknut with a nylon collar that increases friction on the screw thread. |
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Helicoil |
Recoil Insert |
Wire inserts that produce strong, permanent threads in metals and plastics, including softer metals. |
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Lag Bolt |
Hex Lag Screw |
Large wood screws with a hexagon-shaped head. |
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Plaster Washer |
A flat washer originally developed for automotive repair, now used in applications requiring an extra-wide bearing surface. |
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Pop Rivet |
A non-removable fastener. |
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Red Brass |
Silicone Bronze |
A low-lead brass alloy generally composed of 96 percent copper with superior corrosion resistance. |
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Roll Pin / Split Pin / Spring Pin |
Expand and create tension against the walls of holes. When inserted through two or more objects, they fix the relative positions. Used as dowels, spacers, and cotter pins. |
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Shake Proof Washer |
A washer designed to create tension so that the bolt does not loosen from its installed position. Lock washers prevent the rotational movement of the installed bolt. |
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Sheet Metal Screw |
A self-tapping screw that forms mating threads in a pre-drilled hole as it is driven. |
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Stove Bolt |
Used for binding material together by going into a tapped hole or through a hole held with a nut. |
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Stripper Bolt |
A bolt with an unthreaded shoulder that is larger in diameter than the threads. |
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TEK Screw |
Self-drilling screws with drill bit tips that eliminate the need for a separate pilot hole. Commonly used in electrical and roofing applications. |
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Whiz Nut |
Flange nuts with a washer-like base to distribute pressure over a greater surface area and ensure the fastener stays tight. Commonly used in manufacturing assembly lines. |
About Royal Brass and Hose Fasteners
Royal Brass and Hose has been selling fasteners (nuts, bolts, and screws) since purchasing Cornette Fasteners in Maryville, TN in the late 1980s. In 2019, Royal Brass and Hose purchased Hardline Industrial Fasteners in Birmingham, AL. The company currently stocks over 16,000 different fasteners.
For a complete breakdown of the Royal Brass and Hose fastener part numbering system, see: How to Identify Fasteners by Part Number.
Need help with selecting a fastener?
Contact a Royal Brass and Hose sales representative or call 800-669-9650 for help identifying the right fastener for any application. Royal Brass and Hose serves customers across 11 locations: Knoxville, TN; Marietta, GA; Orlando, FL; Charlotte, NC; Little Rock, AR; Fort Worth, TX; Benton, IL; Madisonville, KY; Princeton, WV; Birmingham, AL; and Calvert City, KY.
Frequently Asked Questions About Fastener Slang
Technically, bolts pair with a nut while screws are driven into a tapped hole or directly into material. In common usage, many fasteners are called either depending on the trade or industry. The hex cap screw vs. hex bolt distinction is one of the most common sources of confusion: a hex cap screw has tighter body tolerances and a chamfered end, while a hex bolt does not.
A whiz nut is the informal name for a serrated flange nut. The flange distributes pressure over a larger surface area, and the serrations under the head grip the material to resist loosening from vibration.
Use the slang reference table in this guide to match informal terms to official Royal Brass and Hose part names. If the term is not listed, contact a sales representative. Royal Brass and Hose can identify parts from descriptions, samples, or photos.
Royal Brass and Hose stocks over 16,000 fasteners. Most of the parts listed in this guide are available. For items marked 'N/A' in the part name column, contact a sales representative to confirm availability or find an equivalent.
The site search works best with official part names or part numbers. Use this guide to translate a slang term to the correct name first, then search or browse the category pages to locate the product.
