Whenever you are working with fasteners, you want to be sure you have a strong, durable rivet or bolt that is suited to the job. Blind threaded inserts are among the most versatile types of fasteners, and there are thousands of types from which to choose. Choosing the right threaded insert depends on the nature of the materials you are working with and the application.
What’s a Threaded Insert?
A threaded insert is a sleeve with a threaded interior that can accept a bolt or threaded fastener. The insert can have different dimensions, be made of different materials, and come in different configurations or tooling; its design will hold fast in thin or soft materials, making the threaded fastener secure.
If you have devices that need to be disassembled and reassembled or that use particularly soft materials, threaded inserts offer a number of advantages, especially if the connection is load-bearing. Flexible plastics, for example, have difficulty holding threaded bolts because the threads in the tap hole aren’t durable enough. Rather than relying on threads drilled into the soft workpiece itself, a threaded insert gives you more strength and more versatility and tends to be more resilient over time.
Threaded Inserts Designed with Automation in Mind
Blind threaded inserts can be installed from one side, enabling faster installation, especially in a production line. They offer a stronger alternative to weld nuts and tapped holes, and they provide a stronger bond than self-tapping screws. In fact, threaded inserts are usually the strongest and least time-consuming fasteners used in any manufacturing setting, especially because they were designed for automation.
Threaded inserts have ribbed walls that offer greater strength under load. They can be used at virtually any stage of production, including after a workpiece is painted or coated, because they don’t require reworking once they are installed. That’s why blind threaded inserts have become so popular in applications such as aerospace, defense, transportation, clean energy, medical applications, and electronics.
Types of Threaded Inserts
There are a variety of different types of threaded inserts, each with a different design for a specific application.
- Rivet nut inserts, sometimes referred to as blind rivet nuts, can be installed from one side of a joint and have a counter-threaded interior designed to accept a bolt. Some rivet nuts will bulb on the blind side to create a solid connection. Others are designed to pull the rivet nut into the sleeve as they are tightened.
Rivet nuts were first used to connect thick-walled materials in the 1930s, when RIVNUT® fasteners came into extensive use in aerospace manufacturing. When securing metal, thick-wall threaded inserts are often used. These are the most common types of inserts and come with both ribbed and knurled bodies, as well as smooth bodies in round, hexagonal, semi-hexagonal, and other shapes. They are made of different materials and come in different shapes, including large and small flanged heads, open and closed-end, and other designs.
Thin-walled inserts came later in round, hexagonal, and square designs. These inserts offer added versatility, such as using sealant under the head or special plating for greater durability in harsh conditions.
They also come in a knurled body design for a better grip on the material. For thicker fiberglass materials, such as those used in boatbuilding, knurled inserts are often used to minimize corrosion.
- Eurostyle inserts are round-body threaded inserts with semi-hexagonal, fully hexagonal, heavy hexagonal, or square body designs. They are available from a variety of manufacturers, including Avdel, Atlas, and Sherex Fastening Solutions.
- Slotted body threaded inserts are designed with gashes in the body that expand when the bolt is tightened for a firm connection. Slotted-body threaded inserts are commonly used for thin-gauged metals, such as aluminum. This insert has cuts along the body that come pre-bulbed to collapse on the blind side to secure the insert. There are straight-body and pre-bulbed body types from manufacturers such as Avdel, Atlas, Sherex, AVK, Goebel, and Marson.
- Molly Jack threaded nut inserts are designed for use with thin, brittle, or soft materials and are perfect for the assembly line. They are available in steel, brass, and coated steel, and when tightened, the sides collapse against the hole walls to form a permanent, reusable threaded insert. They can be installed by hand or using pneumatic tools without distorting thin materials. For applications such as securing a circuit board, attaching plastic molding, or working with thin sheets of fiberglass, Molly Jack inserts are often used. Molly Jack inserts are made of thin, brittle material that collapses on the blind side when tightened. There are other types of threaded inserts for plastic, depending on the type of plastic and the application, including ultrasonic heat-staking inserts, push-in inserts, and molded-inserts.
- Stud-style threaded inserts are available for any type of application with different thread sizes, head types, lengths, and materials. Bay Supply carries a variety of stud-style inserts from major manufacturers such as Atlas, AVK, Goebel, and Marson. For wood assemblies, such as furniture, threaded inserts are useful to create firm bonds (e.g., connecting chair or table legs or other joins). They also are used to reinforce stripped joins and for concrete construction applications. In addition to inserts that accept bolts or fasteners, threaded stud-style inserts are similarly secured in the tap hole but are designed to accept a nut.
- Wellnut threaded inserts are useful for sealing holes or limiting vibrations. The wellnut insert is passed through one of the pieces of material and the nut is inserted from the flanged end. The non-flanged end is inserted into the second piece of material. As the bolt is tightened, the flange expands to prevent the insert from turning and the bushing is compressed to form a tight seal around the bolt hole. For watertight applications, a wellnut insert is a good choice. These inserts are made of rubber or neoprene with a threaded metal sleeve insight, and when they are tightened, the rubber draws in to form a waterproof seal.
- Riv-Float® threaded inserts are made by Sherex Fastening Solutions for off-center applications in which two pieces of material need to be connected but the holes fail to align.
Choosing the Right Threaded Insert
In addition to different configurations, threaded inserts also come in different materials for different uses.
Brass inserts, for example, are ideal for wood and particleboard. Threaded plastic inserts are used for applications such as telecommunications and instrumentation because they are nonconductive and the threads create a lasting hold and can be assembled and disassembled with minimal wear.
By contrast, stainless steel inserts are used in molding and metal working, often for repair jobs or manufacturing. Stainless steel is also useful for clean applications such as food and beverage processing because it resists corrosion.
Applications for Threaded Inserts
Once you understand the versatility of threaded inserts, you can start to see the possibilities. That’s why threaded inserts have become common for manufacturing, assembly, construction, and repairs. Here are just a few industries that rely on threaded inserts:
- Aerospace and aviation: The first threaded inserts were used to secure deicers to airplane wings.
- Automotive: Inserts are used throughout car bodies, including wellnuts that use rubber bodies to cut vibration and inserts to secure metal and plastic body parts.
- Boatbuilding: Threaded inserts are used in wooden and fiberglass boats to secure hull and trim. These inserts are made of brass, coated steel, and other materials that resist corrosion.
- Furniture: We reviewed wooden furniture above. Inserts can be used to attach metal to wood, for plastic joins, and for other types of furniture manufacturing and repairs.
- Appliances: Whether they’re securing a plastic cover or circuit board controls, you will find threaded inserts in many household appliances.
- Green energy: Threaded inserts are built to last, and they are commonly used for green energy applications such as securing solar panels or constructing windmills.
Blind threaded inserts are designed for production efficiency as well as durability, and they can be incredibly versatile. If you need help choosing the right threaded insert for the task, an experienced fastener distributor can help you weigh your options and select the right one.
This article was published in April 2019 and updated in June 2020.