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Threaded Inserts for Plastics

Threaded Inserts for Plastics provide reusable threads and preserve the bolted joint integrity for the life of the application. Since an Insert is generally twice the diameter of a screw, the shear surface is increased fourfold, thereby significantly enhancing the load carrying ability of the bolted plastic joint as compared to one without the use of a metal Threaded Insert. Threaded Inserts for Plastics also allow the appropriate installation torque to be applied to the screw without stripping the threads that would otherwise occur if the screw was installed directly into the plastic. In addition, the metal thread of an Insert provides permanent creep resistance for the entire load path of the thread to prevent loosening and maintain a durable tightly threaded connection.

The two main categories of plastics suitable for Threaded Insert installation are thermosets and thermoplastics. Thermoset plastics, once formed, undergo an irreversible chemical change and cannot be reformed using heat and pressure. These plastics are tough and heat-resistant. Examples of thermosets are Bakelite, epoxies, urea and polyester resins. Heat/ Ultrasonic Inserts are not suitable for thermosets since this type of plastic can not be reformed. Thermoset plastics require the use of Molded-In, Press-In, or Self-Tapping Inserts.

Thermoplastics are rigid and solid at normal temperatures, and at elevated temperatures they soften and melt. Some of the more common thermoplastics are ABS, polyamide (eg. Nylon 6-6), PVC and polycarbonate (PC). Press-In, Self-Tapping, Heat / Ultrasonic and Molded-In Inserts are suitable for plastics in this category.

SPIROL’s Inserts are designed to maximize and balance rotational torque and tensile (pull-out) performance. Attention to knurl and thread quality further enhances performance. SPIROL offers a comprehensive line of Threaded Inserts for Plastics to suit the installation method, plastic type and performance requirements of your specific application.

If installation equipment is required, SPIROL also offers a standard comprehensive line of Insert Installation Equipment from manual to fully automatic modules, with or without out fixturing, to support your Threaded Insert assembly requirements.

Application Engineering Assistance: If you would like assistance in selecting the proper Threaded Insert - including the recommended hole size, tolerance and boss diameter for your plastic assembly and mating component, please Request Technical Support! We are here to help!

Threaded Insert Types

SPIROL offers a variety of Threaded Inserts for Plastics to meet your performance and installation requirements including Press-In, Self-Tapping, Heat / Ultrasonic and Molded-In Inserts in standard thread sizes ranging from M2 (2-56) to M8 (5/16-18) – depending on Insert type.

  • Press-In Inserts are installed by simply pressing the Insert into a molded plastic hole. Ideal for use in softer plastics, Press-In Inserts provide a reusable thread to meet the tightening torque requirements of a threaded joint. SPIROL's Press-In Inserts are available with or without a head, and offer moderate pull-out and good torque resistance.
  • Self-Tapping Inserts are installed by rotating the Insert into a molded plastic hole. Driven by its internal thread, Self-Tapping Inserts either cut or form their own threads during installation into the hole. Self-Tapping Inserts can be used in both thermosets and thermoplastics.
  • Heat/Ultrasonic Inserts are designed for post-mold installation in thermoplastics. Heat and ultrasonic installation of these Threaded Inserts yield outstanding performance results. Available in long and short variations, long for maximum torque and pull-out resistance; short for less stringent requirements with the benefits of lower cost and reduced installation time.
  • Molded-In Inserts are placed over core pins within the mold cavity as a part of the molding process. As the plastic is injected into the mold, it flows around the periphery of the Insert filling the knurls, barbs and undercuts of the Insert's external design providing torque and pull-out (tensile) resistance. Molded-In Inserts can be used in thermoplastics and thermosets.


If one of SPIROL's standard Threaded Inserts does not meet your needs, our Application Engineers will work with you to design a custom Insert to meet your unique requirements.

Select from the options below for more specificity about the different types of SPIROL's Threaded Inserts for Plastics or contact us for complimentary technical support!

Don't See What You're Looking For?

Need help choosing the most appropriate fastening solution for your application? SPIROL's Application Engineers will review your specific requirements, and design the most cost-effective Threaded Insert to meet your technical and commercial needs. Let us help!

Request Engineering Support


SPIROL's standard Inserts are manufactured from aluminum or brass (depending on the Insert type) and have a plain finish. Additional materials and finishes can be evaluated upon request.

Material Type Material Grade
A  Aluminum - High Strength Aluminum Alloy ASTM B211 2024
ISO AlCu4Mg1
E  Brass - Free-Cutting Brass ASTM B16
UNS C36000
EN 12164 CW603N CuZn36Pb3

RoHS compliant    
TO ORDER: Product Code (Series #) / Thread Size / Length / Material / Finish    
EXAMPLE: INS 19/M5 / .250S EK    

Full Specifications

Design Guidelines

SPIROL provides general design guidelines to help select the most appropriate Threaded Insert for your specific plastic assembly. Each application has unique considerations such as the specific plastic type in which the Threaded Insert will be used, torque and tensile requirements, corrosion resistance, temperature requirements, and installation methods.

SPIROL’s design guidelines encompass general recommendations for:

  • Hole diameter and draft angle
  • Hole size adjustment based on percentage of filler content
  • Hole depth
  • Installation depth of Insert
  • Optimal wall thickness / boss diameter
  • Clearance hole diameter for mating component

Access Design Guidelines for Threaded Inserts

SPIROL offers complimentary Application Engineering support to not only help you select the most appropriate Threaded Insert for your plastic assembly, but to also help you design your assembly to achieve the desired performance for the life of the project. Feel free to contact us at any time to engage our Application Engineering Team!

Design Guidelines

Insert Testing & Performance

The correct installation settings are critical to Heat/Ultrasonic Insert performance. The tapping process for Self-Tapping Inserts has to be set to avoid hole reaming. Improper installation can have devastating effects on performance.

The following factors impact Insert performance:

  • Insert type, design with type and quality of the Insert features,
  • Plastic material and filler composition,
  • Design and quality of the plastic components including hole consistency,
  • Installation process and resultant quality, and
  • Alignment of the mating component and how it supports the installed Insert.
Testing & Performance Data
Your Total Assembly Solution

Installation Technology for Threaded Inserts

In addition to a comprehensive line of engineered components used for joining and assembly, SPIROL also offers a full range of Installation Equipment for Threaded Inserts for Plastics specifically designed to facilitate cost-effective and high quality assembly of your products.  Our installation solutions range from manual machines to fully automatic work cells with statistical process control and error-proofing options.  We are the only company of our kind that offers the total integrated solution. 

Explore Threaded Insert Installation Equipment

Local Design, Global Supply.

SPIROL has Application Engineers throughout the world to assist you in your designs, supported by state-of-the-art manufacturing centers and worldwide stocking facilities to simplify the logistics of delivering your product.

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