February 10, 2021

The Primary Types of Threaded Fasteners

Currently, there are more than 300 billion threaded fasteners used in the United States annually. These fasteners are utilized in a variety of ways including complex manufacturing processes, commercial construction projects, or even just anchoring bookshelves at home. Considering the wide range of fastener options, it’s important to understand the primary types of fasteners before choosing one for your application.

What Are Threaded Fasteners?

Threaded fasteners are most easily identified by either an external or internal screw thread.

All threaded fasteners share a simple but essential function: to fasten objects together and hold components in place.

While there are many ways to join components including welding, adhesives, and brazing, threaded fasteners are a very popular choice as they are a non-permanent solution that can be installed, tightened, and removed quickly. They are also much stronger than unthreaded fasteners, like rivets, grommets, and pins.

Threaded Fastener Classifications

Threaded fasteners can also be classified by their thread length. There are fully threaded fasteners that have threading from the head to the tip and partially threaded fasteners that have threading on only part of the shaft.

Fully threaded fasteners can withstand greater force and are best for grip strength because tension is spread over the entire fastener. Partially threaded fasteners are better for alignment and shear strength, and a partially smooth shaft on nuts, bolts, and screws makes them ideal partners for washers.

Common Types of Threaded Fasteners

The three primary types of threaded fasteners are nuts, bolts, and screws. Most fasteners are made of stainless steel or carbon steel, however there are also threaded fasteners made from other metals or alloys including titanium, copper, aluminum, nickel, and bronze.

Screws

A screw has a slotted head that allows you to twist its pointed end into material to fasten two objects together. You use a screwdriver or drill to install the screw into wood or other material. The most common screw heads are:

Phillips head: Features a cross-shaped slot on the screw head
Flathead: Similar to Phillips head, except it has one horizontal slot
Hex: Features a hexagon-shaped slot on its head
Torx: Features a star-shaped slot on its head

There are dozens of types of screws, but most fall into two broad categories: screws that require you to drill a pilot hole before installing the screw and so-called self-drilling screws that don’t require a predrilled hole. Some common types of screws include:

Wood screws: These screws—which are made of metal—are designed to connect two or more wood pieces. Typically, they’re self-driving screws partially threaded with a smooth upper shank to prevent the screw head from driving deep into the wood. Many homeowners use some variation of wood screws for a variety of purposes.
Masonry screws: These screws have a flat tip and require a predrilled hole. Most masonry screws have hex heads that are raised instead of slots. You can use them for attaching wood to concrete or metal.
Sheet metal screws: These screws are fully threaded with sharp points to drive into metal, wood, or hard plastic.
Lag screws: Sometimes called lag bolts, these sturdy screws have a square or hex head and are typically driven with a wrench. You use them for heavy applications like roofing.
Machine screws: There are a wide variety of machine screws that are used in machining and manufacturing applications. They are ¼ inch or less in diameter, and their primary use is to hold metal objects together. Manufacturers design them to fit precisely with the parts they will fasten.

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Bolts

Most bolts are threaded only at the flat end of their shaft. The primary difference between bolts and screws is that bolts require a nut to create tension and screws don’t. In addition, screws are not meant to pass completely through the material while bolts must pass all the way through in order to make a connection with the nut. Common types of bolts include:

Carriage bolts: Featuring a round head without slots that you secure in place with a nut, it’s commonly used to fasten wood with wood or wood with metal.
Hex bolts: These versatile bolts have hex heads that are useful in tight spaces.
Stove bolts: This general-purpose bolt has a slotted head that allows you to use a screwdriver to fasten it to a bolt. Their shafts are almost fully threaded.
Machine bolts: Most have hex heads and require you to use a wrench or socket to fasten them. They’re commonly used to secure wood with wood or wood with metal.

Nuts

Nuts are circular-shaped or hex-shaped pieces of metal with a threaded interior surface. Nuts are used in conjunction with bolts to fasten parts together. Some common types of nuts are:

Dome nuts: Also known as acorn nuts or cap nuts, they have a distinctive domed top. These nuts often are used for aesthetic purposes because they cover the threaded end of a screw or bolt.
Hex nuts: These nuts are hexagons with six sides. They are multipurpose nuts that you can use with most types of fasteners. Some common hex nuts include:
- Hex finish nuts: The most used nut worldwide, they fasten with bolts to create a tight joint for many common applications.
- Hex jam nuts: A thin nut about half the thickness of a regular hex nut and “jammed” against a hex nut on a bolt. You tighten the bolts against each other rather than against the material’s surface to protect the material from damage.
- Heavy hex nuts: A hex nut made with thick walls to support heavier loads.

Serrated flange nuts: These are hex nuts with an integrated wide flange washer that doesn’t spin or move. Serrations under the washer provide a locking action that prevents the nut from loosening from the fastener. Because of the serrations, you shouldn’t use these nuts on surfaces vulnerable to scratches.

Producing Custom Threaded Fasteners

While you can walk into any hardware store in the world and find a wide range of threaded fasteners, the off-the-shelf options may not always be what you need. When it comes to large scale industrial projects, product prototyping, or aerospace applications, sometimes the only option is a custom threaded fastener.

Here at The Federal Group USA, we have been producing custom fasteners for more than 40 years. We specialize in a wide range of metal fabrication services including casting, machining, cold forming, and much more.