Threaded Inserts

A threaded insert is a precision-engineered, cylindrical component, typically metallic, featuring a precisely formed internal thread. Its primary function is permanent installation into a pre-prepared hole within a parent material – such as plastics, woods, composites, or soft metals. This process establishes a high-strength, wear-resistant, and reusable threaded receptacle where direct threading would be inadequate.

Beyond new installations, these versatile components are also critically employed for two key purposes. They reinforce existing threads in high-stress applications, providing added durability. Furthermore, they offer an efficient and lasting solution for repairing stripped or compromised threaded holes, predominantly in metalworking environments. This capability restores structural integrity without requiring extensive component replacement or custom fasteners.

Ultimately, threaded inserts significantly enhance pull-out resistance, torque-out performance, and overall joint integrity in applications where direct threading would otherwise be unreliable.

How to Fit a Threaded Insert

Proper installation is key to maximising performance. The process involves two main steps, depending on the insert type and material.

First, precisely drill, mill, tap, or cut the recommended hole size into the material. Accuracy here is paramount for a secure fit.

Second, the installation method varies:

• Press-fit inserts: Pressed directly into the hole, common in softer materials like some plastics or woods.
• Thread-in (self-tapping) inserts: Screw into a pre-drilled hole, cutting their own threads, effective for plastics and softer metals.
• Heat-set inserts: Heated and pressed into thermoplastics; the melted plastic solidifies around the insert for a strong bond.
• Expansion inserts: Expand upon installation, creating a strong grip, effective in softer materials.
• Key-locking inserts: Screwed into tapped metal holes, then keys are driven in to prevent rotation, ideal for high-stress applications or repairs.

Types of Threaded Inserts

Threaded inserts are meticulously designed to provide strong, reliable threads in a vast array of materials, each type optimised for specific material properties and application requirements. Understanding these distinctions is crucial for selecting the correct fastening solution for your project.

For Plastic

Plastics are broadly categorised into two main types: thermoplastic and thermoset. These materials possess distinct physical characteristics, necessitating different threaded insert designs and installation methods.

Thermoset

Thermoset plastics undergo cross-linking of polymers during curing, resulting in improved physical and mechanical characteristics. This makes them typically simpler to mill and drill. Consequently, press-fit threaded inserts are frequently favoured for these materials. This choice is driven by the easy installation and firm grip achievable within the strong, rigid structure of thermosets.

Thermoplastic

Threaded inserts for thermoplastic are installed by heating the insert and pressing it into the plastic. The heat melts the plastic, which then cools and solidifies around the insert, forming a strong bond.

For Metal

Threaded inserts for metal are primarily designed to strengthen existing threads or to efficiently repair damaged threads in metal components. These inserts typically feature an external thread. The insert is simply matched by its internal and external thread size and then carefully screwed into the existing, often damaged or worn, threaded hole. This process effectively restores the integrity of the connection, providing a durable and reliable thread for subsequent fastenings.

For Wood

Both press-in and thread-in (self-tapping) threaded inserts in wood are possible. For hardwood, which can crack, a slightly larger pilot hole with adhesive is advised for durable wood threaded inserts solutions.

Materials and Finishes

Threaded inserts are available in a variety of materials and finishes, with metric coarse threads being standard, designed to suit virtually every application and environmental condition. The material choice significantly impacts the insert's strength, corrosion resistance, and compatibility with the host material.

Common materials include:

• Brass: Corrosion-resistant, good conductivity, easy to machine (brass threaded inserts).
• Steel: General-purpose strength and durability.
• Stainless steel (316 & 302): Excellent corrosion resistance for harsh environments.
• Aluminium: Lightweight and corrosion-resistant.

Common finishes include:

• Bright zinc plated: Good corrosion resistance, clean aesthetic.
• Clear passivated: Enhances stainless steel corrosion resistance.
• Galvanised: Durable, corrosion-resistant coating for outdoor use.
• Plain: Uncoated, for further treatment or non-corrosive settings.

Thread Sizes

Threaded inserts are available in a comprehensive range of standard metric coarse thread sizes to fit various fasteners.

Common sizes include:

• M3, M3.5, M4, M5, M6, M8, M10
• And larger sizes for heavier duties.
• Choosing the correct thread size is crucial for compatibility and achieving desired joint strength.

Factors to Consider When Choosing Threaded Inserts:

Selecting the ideal threaded insert requires a thorough understanding of your application's specific demands. Careful consideration of these factors will ensure you choose the right product for optimal performance, reliability, and cost-effectiveness.

• Base material: Identify the host material (e.g., wood, plastic, metal); this dictates the insert type.
• Load requirements: Determine anticipated pull-out and torque-out loads to ensure the joint withstands forces.
• Insert material and finish: Choose material (e.g., brass threaded inserts, steel, stainless steel) and finish for strength, corrosion resistance, and compatibility.
• Installation method: Match the insert type to your preferred installation (e.g., press-in, heat-set, self-tapping).
• Thread size and type: Ensure the internal thread matches your fastener; consider coarse or fine.
• Environmental conditions: Account for temperature, vibration, chemicals, UV, or moisture.
• Cost-effectiveness: Balance cost against performance and added value to your product.

Applications of Threaded Inserts

Threaded inserts are incredibly versatile fastening solutions, finding crucial applications across a vast array of industries and everyday products. Their ability to provide strong, reliable threads in diverse materials makes them indispensable for modern manufacturing and repair.

• Metal fabrication and repair: Used to repair stripped threads or create strong threads in softer metals.
• Plastic components: Essential for robust, reusable threads in moulded plastic parts (e.g., electronics housings).
• Automotive industry: Extensively used in vehicle manufacturing for durable, maintainable fastening points.
• Manufacturing and assembly lines: Facilitate efficient assembly of components, especially with dissimilar materials or frequent disassembly.
• Woodworking & furniture manufacturing: Threaded inserts for wood (including screw inserts for wood) create strong, reusable connections in timber for furniture and cabinetry; a key tool for woodworking vice users.
• Electronics and electrical enclosures: Provide secure mounting points for PCBs and components within enclosures.

Find the Perfect Threaded Insert for Your Project

The right threaded insert is fundamental for strong, durable, and reliable fastened connections. Selecting the correct threaded insert is key to optimal results, whether for timber, plastic, or metal.

As your trusted partner for industrial fasteners, RS NZ offers an extensive range of threaded inserts from leading global brands. Explore our online selection today to find the ideal threaded insert solution to empower your team for secure, long-lasting assemblies.

Ordering & Delivery Information for NZ

RS New Zealand, a division of the RS Group, provides a comprehensive selection of industrial components sourced from reputable manufacturers, including RS PRO, Samtec, Phoenix Contact. Our user-friendly website facilitates efficient product discovery and procurement, accessible at any time.

Our website also features a wide variety of handy tools like coaxial cable connectors, cable glands, and lead screw nuts, alongside other essential accessories. We provide dependable nationwide delivery throughout New Zealand, with a commitment to expedited shipping. For more details on ordering, delivery, and fees, please visit our delivery page.