Threaded inserts are some of the most versatile fasteners ever invented. They can be used in virtually any material to create a strong join that can accept a bolt or screw, they can be made of various materials, and they have come into common use in a wide range of industries and applications.
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.
There are different types of threaded inserts for different types of materials. Most inserts are fitted into predrilled or tapped holes; in fact, they are extremely useful for repairing stripped threaded holes. For soft materials, such as plastic or wood, the threaded insert often has a shaped or ridged body to hold itself in place and prevent it from turning. Once it is inserted through the hole, the insert is secured by tightening the insert to create a bulb on the blind side to secure it in place, or by tightening the bolt to draw the insert back into itself to secure it in the hole.
For thinner materials, threaded inserts usually are secured by collapsing the sides of the insert on the blind side to secure it in place with a flange. When inserted through the hole, the body of the insert collapses to create a strong bond that won’t pull through the material under load.
Matching the Right Threaded Insert to the Material
Because they are so versatile, threaded inserts can be used to secure a wide range of materials. Here are some common examples:
- Plastics: For soft or brittle materials, such as plastics, threaded inserts provide a secure join that can be assembled and disassembled as often as required. For applications such as securing a circuit board or attaching plastic molding, 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.
- Wood: Soft woods and composites such as pine and plywood are good candidates for threaded inserts. For wood assemblies, such as furniture, threaded inserts are useful to create a firm bond, such as with chair or table legs or other joins. They also are used to reinforce stripped joins. 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.
- Fiberglass: Fiberglass presents a unique problem. For thin sheets of fiberglass, Molly Jack inserts are useful, but for thicker fiberglass materials, such as those used in boatbuilding, knurled inserts are often used to minimize corrosion.
For watertight applications, a wellnut insert may be a better choice. Wellnut 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.
- Metal: 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.
For thin-gauged metals, slotted-body threaded inserts are used as well. The slotted-body insert has cuts along the body that come pre-bulbed to collapse on the blind side to secure the insert.
- Aluminum: Because aluminum can be thin and brittle, slotted-body inserts are often best for this material. There also are threaded inserts made of aluminum for special applications.
- Concrete: Construction using concrete often requires securely connecting steel beams to foundations and similar applications. For concrete construction, stud-style inserts are commonly used, as well as thick-wall threaded inserts.
A Variety of Industries That Use Threaded Inserts
Once you understand the versatility of threaded inserts, you can start to see the possibilities. That’s why threaded inserts have become commonplace 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 the car body, 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, and are made of brass, coated steel, and other materials that resist corrosion.
- Furniture – We reviewed wooden furniture above, but 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.
Any application in which you need to securely join two pieces of material is a likely application for threaded inserts. With so many options, it can be overwhelming to figure out which threaded insert you need, but an experienced fastener distributor can recommend the right types of inserts and tools for you.