Why Coil Thread Inserts Are Unique Among Fasteners

Threaded fasteners need a solid substrate for lasting performance. The threads must be solidly anchored in the material without loosening or pullout, which can be challenging with softer materials, such as wood and plastics. Threaded holes can also become stripped over time, requiring some way to restore the threads.

Coil thread inserts offer an innovative solution to provide a strong tapped hole. They also extend the load of the fastener from the first three threads to the entire length of the insert.

What Are Coil Thread Inserts?

Coil thread inserts, sometimes called helically wound inserts, are wound coils that screw into a stripped tap hole or soft materials to accept a threaded fastener. The coil should be slightly larger than the hole to provide a snug fit. The insert is screwed into place to provide a firm footing for a threaded fastener. Screwing the right-sized bolt or fastener into the coil pushes the coil against the walls of the hole, and the outward pressure of the fastener forms a joint that won’t loosen or pull out.

For softer materials, such as soft woods, fiberglass, and plastics, a coil insert can create a stronger joint than a rivet nut threaded insert. Coil thread inserts also reinforce softer metals, such as aluminum, to repair stripped steel threads, including those found in automotive cylinder heads, and for use in construction projects involving concrete.

Tanged and Tangless Coil Thread Inserts

There are two basic designs of coil thread inserts—tanged and tangless—and each is designed to provide a reliable means to screw the coil into a hole.

Tanged Coil Inserts

Tanged coil inserts have a straightened piece of the coil, or “tang”, at one end that is used to install the insert. A special tool grips the tang and uses it to screw the coil into the hole. The tang is then snapped off to complete the installation, which leaves excess metal that must be collected.

There are two basic types of tanged coil inserts. Tanged free-running coils allow the fastener threads to adjust to the coil independently, resulting in a stronger bond because the thread distributes the load across the entire surface. 

Tanged screw-lock coil thread inserts feature a slightly different design, incorporating straightened segments as part of the coil. When the threaded fastener is inserted, those straightened segments flex outward to put pressure on both the threaded fastener and the parent materials.

Tangless Coil Inserts 

Tangless coil thread inserts are gaining in popularity because they are easy to install and require no tang or metal to remove. Tangless coils have a notch on one end that serves as a grip point, allowing them to be installed and inspected quickly without excess metal that could get into machinery. They can also be adjusted and removed more easily after installation.

Tangless coil thread inserts are also available in free-running and screw-lock configurations.

Threaded Inserts for Every Application

The Heli-Coil® from STANLEY Engineered Fastening is one of the best-known wire-threaded inserts and is available in both tanged and tangless configurations. The Heli-Coil is available in a range of sizes and materials, including specialty inserts for pipes, spark plugs, and self-tapping inserts. STANLEY also offers a range of power and manual installation tools.

KATO Fastening Systems offers a full complement of tanged and tangless coil inserts and tools. There are more than 5,550 KATO parts, tools, and products designed for fast installation and reduced costs available on the Bay Supply Marketplace. 

KATO wire threaded inserts are available in various materials for different applications. Inconel® X-750 inserts are made from a nickel-chromium alloy hardened by the addition of titanium and aluminum for high-temperature applications. Nitronic 60® inserts have silicone and manganese to minimize friction when used with stainless steel screws and bolts. Nimonic 90® is a nickel-chromium-cobalt alloy designed for extreme heat and pressure. KATO also makes phosphor bronze inserts that resist corrosion in salt water and titanium coil inserts that deliver a superior strength-to-weight ratio. 

Recoil tangless helical inserts from Arconic are one of Bay Supply’s most popular threaded inserts. They’re available in free-running and screw-lock designs. Free-running inserts are fast and easy to install using power or hand tools. They are also available in a strip-fed configuration with a plastic ribbon that is fed through an assembly nozzle for factory use.

Recoil inserts are available in a range of materials, including stainless steel (grades 304 and 316), Inconel® X-750, phosphor bronze, Nimonic 90®, and Nitronic 60®, so they can be used in various applications, including shipbuilding, power, manufacturing, consumer electronics, automotive, aerospace, and more.

Arconic also offers a range of lubricants and coatings. Silver plating increases performance for high-temperature applications, such as when used in aerospace engines. Cadmium plating reduces corrosion in salt water for marine applications. Tin plating is specified for moderately corrosive applications, such as for use in automobiles. There are also dry film lubricants and color coatings for identification.

No matter the application, the Bay Supply Marketplace has the coil thread inserts for the job. See the complete catalog, and be sure to review The Essential Guide to Coil Thread Inserts.