Damaged threads are one of the most annoying issues in metalworking. In most cases, they have a piece of a bolt that has to be removed, which only increases the risk of further damage. There are also repairs, drilling, re-tapping, and processing of the adjacent assembly parts to match the new thread.

Today's article will discuss threaded inserts for metal, what they are, how they work, and what different types and variations of the product exist on the market.

 

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What Are Threaded Inserts for Metal?

Threaded inserts are cylindrical tube-shaped pieces of metal with an internal and external thread. They're designed that way to strengthen or repair damaged threads in metalwork and still provide a threaded receptacle for bolts, screws, and other fixings.

They're ideal for repairing or reinforcing threaded holes in soft metals, such as aluminum, magnesium, brass, or cast iron. External threads are standard size and pitch, allowing for a straightforward installation using standard drills and taps. In addition, most manufacturers like, E-Z Lok, Heli Coil, Acme Industrial make threaded inserts in a way that allows easier fastening, either with a screwdriver, bolt/jam nut, an Allen wrench (or hex key), or optional power tools.

Additionally, some manufacturers pre-apply microencapsulated adhesive onto external threads, which begins to set immediately upon installation. In most cases, it also provides a gas and liquid seal after it's fully cured.

It's worth noting that threaded insert nuts can be removed, unlike mechanically-locked pins, which usually need to be drilled out. In most cases, you're just required to screw them out of place or use a bolt extractor. If you use a self-locking (adhesive) threaded insert, you can also heat the thread to release the adhesive.

Types of Threaded Inserts for Metal

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The use of key locking threaded inserts for metal exceeds just the thread repair; they're great if you're working with thin materials that require a strong and durable fastener. However, their application largely depends on their type since not all threaded inserts are the same.

Thin-Wall Rivet Nut

Rivet nuts, also known as rivnuts or nutserts, create a load-bearing nut and bolt threads in application in which the base material is too thin to apply threads. They're also known as blind threaded inserts, as they don't have any external threading but a smooth or knurled outer surface.

During the installation process, the body collapses on the backside and grips the inside of the mounting surface. They feature standard thread sizes and can be mounted in drilled holes using most standard installation tools, such as screwdrivers, hex keys, or other power tools.

Solid-Wall Threaded Inserts

Besides having internal threads acting as receptacles for screws and bolts, solid wall inserts have external threads which fasten them in place. Solid-wall inserts are usually sold as part of the thread repair kit for thick-wall applications or applications in which you can tap the base material. In addition, some solid-wall inserts operate as self-tapping elements, which don't require a tapped hole for mounting purposes.

External threads tend to be layered with adhesive, which acts as a fastener. However, some solid-wall inserts employ other fastening mechanisms to stay in place. For example, if you're repairing damaged threads, instead of boring and expanding and re-tapping the existing hole, you can insert helical elements into the existing damaged thread.

These elements, like E-Z Lok or Heli-Coil systems, compensate for any lack of material within the thread and allow for secure fastening of another element without re-threading the mounting surface.

Slotted Body Inserts

Slotted body inserts feature a round, slotted body with a straight or pre-bulbed shank that offers increased spin-out resistance when the insert “collapses”. Working on the same principle as rivnuts, slotted inserts offer a large grip area for single, variable, or multiple thickness materials, though they typically work best with sheet metal and soft metal applications. Besides a fantastic spin-out resistance, and thanks to the very large backside footprint feature, the slotted inserts also have a very good pull-out resistance.

Stud Inserts

Stud inserts are actually composed of a rivet nut body and a "male" threaded stud extending beyond the workpiece. This allows the installer to skip a step in adding a bolt. Instead, you can use traditional threaded hex fasteners. These are ideal for thin walls and provide a more affordable alternative to weld studs.

Applications of Threaded Inserts for Metal

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Thanks to their versatility, threaded inserts can be used in a variety of different applications, which is why they've become so common for the manufacturing, assembly, construction, and repair industries.

However, their use is typically dictated by the different types and materials they're made of. For example, brass inserts are ideal for wood and particleboards, and plastics are used in environments that require electrically non-conductive fastening.

By contrast, stainless steel inserts, mostly made of 303 stainless steel, are often used in metalworking, manufacturing, and repair jobs due to their corrosion resistance and longevity.

Aerospace and Aviation

The first threaded inserts in aviation were used to secure de-icers to airplane wings. These days, almost all structural assemblies use rivets and threaded inserts, as they help aerodynamics and won't jeopardize the structural integrity of the components due to thread damage. 

Automotive

The automotive industry usually relies on carbon steel or zinc-plated threaded inserts in a myriad of applications, from interior vehicle fastening to exterior plastic-trim components and even some electro-mechanical assemblies in your vehicle. They're also used throughout the car bodies, in the form of well nuts, which are rubberized inserts that cut vibrations and secure metal to a plastic body.

Boatbuilding

Often used to secure the hull and trim, threaded inserts used in boatbuilding are often made of brass, coated steel, and other corrosion-resistant material.

Furniture

Threaded inserts for furniture are mostly made of brass or zinc-plated cast metal and feature a hex drive flange, which allows carpenters to install them using a hex drive tool. In addition, they feature a knife thread for fastening into wood, which is notably different from the metric thread used in machining and metalworking.

It should be kept in mind that, in most cases, threaded inserts for metal work fine in woodworking applications, as long as you use ones with a knife instead of metric threads. They're mostly used for attaching handles and knobs, though they can be used in structural assembly.

Appliances

Threaded inserts are used in household appliances, usually to secure plastic covers or circuit board controls. They're also used in home computers to secure the motherboard to the case, establish a good ground connection, and prevent any ESD damage done to your computer.

Green Energy

Threaded inserts are built to be long-lasting solutions, so they're commonly used for green and clean energy applications, such as attaching solar panels in windmill constructions.

Food Industry

The food industry relies heavily on food-grade stainless steel, more specifically, the 304L and 316L stainless steel materials. These types of steel can be welded, but accessibility can pose an issue. What better way to create a threaded hole in a 12 gauge sheet of stainless steel than to use a stainless steel threaded insert?

Common Features of Threaded Inserts for Metal

Though there are several different types of threaded inserts, most of them have several common features and some notable differences. This section will go over common features shared by all threaded inserts and some distinctions tied to specific uses.

Strength

Regardless of the application, threaded inserts for metal are made with specific strength factors in mind. Resistance is the key strength factor when it comes to any type of inserts, and pull-out and torque-out are the two defining parameters of strength.

·        Pull-out force — The force required to pull the insert out of the parent material. This usually refers to the thermal- or press-fitted inserts or previously mentioned thin-wall inserts.

·        Torque-out force — The amount of torque required to turn the insert without inducing any clamp load (a force that holds the joint) on the fastener. Some threaded inserts have adhesive on their outer thread, which fully cures within 48 to 72 hours.

      In most cases, these can be removed with a bolt extractor, which can easily overcome the torque-out force produced by the adhesive component. If allowed by the surroundings, heating the inserts can also release the adhesive.

Easy to Install

Threaded inserts are made with ease of use in mind and are usually very easy to install.

·        Thin-wall insert installation requires very little preparation. Just drill the necessary holes, insert the fastener, and lock it in place according to the manufacturer's instructions.

·        Press-fitted inserts are used in thick-wall applications and usually require very little prep but rely on a hand press that presses them into place. The mounting hole doesn't require any threading, and they're fully locked into place once the fastener has been secured.

·        Thick wall inserts require some prep in terms of drilling and tapping the hole or using a helical insert to repair damaged threading. These usually have some sort of adhesive that secures them in place and acts as a sealant, or they're secured in place via locking pins.

Self-Locking, Vibration, and Sealing

Adhesives, locks, and pins on threaded inserts lock the screw in place and counteract any vibrations and possible loosening of the bolts and screws. This makes them easy to use, as they'll stay in place in case you need to unscrew and remove whatever you screwed in place. In addition, the adhesive prevents them from loosening due to vibrations and thus prevents any potential mechanical and electrical damage.

Additionally, adhesives found on the outer diameter usually serve as a sealant against liquids and gasses. When fully cured, certain adhesives provide sealing of up to 6000psi of pressure (413 bars). If the insert uses a mechanical self-locking method, you can opt to purchase a sealing compound. Additionally, you can opt to use a rubber gasket (it might be provided with the inserts).

Benefits of Threaded Inserts for Metal

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Some parts of the previously assembled workpieces must be dismantled and reassembled, often several times repeatedly. Blind threaded inserts are ideal for use with flexible plastics and thin or brittle materials that require load bearing threads.

An operator, in most cases a technician, can complete an installation or an assembly by using threaded inserts. These small elements allow massive production lines to work faster and more efficiently, as they rely upon only one type of fastener for each connection point to complete the assembly. Considering how time-consuming welding, hole-tapping, and drilling are, threaded inserts provide a quicker way or fastening.

In addition, the knurled or threaded walls of the inserts for metal offer a high level of fastening, capable of withstanding massive amounts of force. Not only that, but they are suitable for automation and ideal for every stage of the manufacturing process. They usually require no finishing touches, like painting or galvanizing, unless specified by the manufacturing process.

Potential Drawbacks

Threaded inserts for metal don't have any potential drawbacks when used for the intents and purposes they're manufactured for. However, it's worth pointing out that not all manufacturers are the same, and some make higher-quality inserts than others, using higher-quality materials and production processes.

This will reflect the final price, so take your application into account when purchasing threaded inserts. You need inserts that are easy to install and durable enough so not to create issues, regardless of whether you're using them on the assembly line or for workshop and repair work

Summary

Threaded inserts for metal provide a fantastic way of joining two pieces of metal and/or other materials, such as plastics and composites, whether we're discussing the automotive industry or solid-wall assembly parts. If you're looking to purchase threaded inserts or learn more about threaded inserts for metal, visit Reid Supply, a global industrial parts supplier. Their expertise in the field will likely help you find what you're looking for.