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Inserts for Plastics
Inserts for plastics are engineered components designed to provide strong, durable, reusable threads inside both thermoplastic and thermoset parts. With the increasing use of plastics in engineering, inserts for plastics help ensure reliability, performance, and cost efficiency. Choosing the right insert depends on plastic type, part geometry, load requirements, and production method.
PRODUCT SELECTION GUIDE
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PRODUCT INDEX
KEY SELECTION CRITERIA
When selecting inserts for plastics, consider the following:
- Type of plastic: Thermoplastic vs thermoset, hardness, and sensitivity to stress.
- Load types: Pull-out strength, torque-out resistance, and jack-out load.
- Boss geometry and wall thickness: Sufficient plastic around the insert to provide proper support.
- Hole design and tolerances: Tapered vs straight, molded vs drilled, and correct chamfering.
- Installation method: Press-in, heat-staking, mold-in, or tapping, depending on the application and production volume.
Popular Insert Types & Features
| Insert Type | Best Use / Key Advantages |
|---|
| Tech-Sonic | High torque and pull-out resistance with opposed knurls and vanes; suited for medium and hard thermoplastics. |
| Sonic-Lok | Quick installation by heat or ultrasonic methods; ideal for speed and strength in thermoplastics. |
| Taper-X | Designed for tapered holes with angled splines for higher torque and pull-out performance. |
| Mini-Tech | Miniature insert for small applications; allows use of small screws with reduced risk of thread damage. |
| Heat-Lok | Suitable for notch-sensitive plastics; smooth knurls reduce stress concentration. |
| Press-Lok / Fin-Lok / Spiro | Optimized for easy press-in installation or for brittle and thermoset plastics. |
| Screw-Sert | Self-tapping insert for post-mold installation, good for plastics with lower core strength. |
| Mold-Form | Installed during molding for a flush finish and high performance, ideal for high-volume production. |
When & How to Use Inserts
Ideal applications include:
- Plastic parts that need repeatable assembly and disassembly
- Components exposed to vibration, thermal cycling, or torque loads
- Projects demanding high-integrity threads such as in automotive and electrical enclosures
Key considerations:
- Inserts add cost and extra process steps
- Over-tightening screws may damage the plastic or cause stress cracks
- Thin walls or poor boss geometry reduce performance and reliability
Best practices:
- Test inserts for plastics early during prototyping to confirm performance.
- Specify holes with the correct tolerances and chamfers.
- Select the right installation method for the material and production scale.
- Ensure boss design supports loads without distortion.
- Use engineering support and data to match inserts for plastics to the intended application.
Enhance Your Assembly with Our Precision Inserts for Plastics
Start browsing our products or request a quote today to find the ideal fastening solution for your application.Frequently Asked Questions About Inserts for Plastics
What are inserts for plastics?
Inserts for plastics are separate threaded metal components installed into a plastic part to create a strong, durable, and highly reusable threaded socket. Unlike direct screw fixings, which form their own thread by displacing the plastic, inserts provide a hardened steel or brass thread interface that significantly outperforms a thread formed directly in the plastic itself.
What plastic materials are suitable for threaded inserts?
Threaded inserts are compatible with most thermoplastics, including ABS, polycarbonate, nylon (PA), acetal (POM), polypropylene, and glass-filled engineering grades. The specific insert type and installation method should be matched to the plastic’s melting characteristics, hardness, and the production volume — PSM’s design guide details which insert type and installation method suit which plastic family.
What is a heat-staked (thermal) insert?
A heat-staked insert is installed by heating the insert and pressing it into a pre-molded hole in the plastic part. The heat softens the surrounding plastic, allowing it to flow around the insert’s knurled or barbed exterior. As the plastic cools, it solidifies around the insert, locking it permanently in place. This method is widely used for thermoplastics in low-to-medium volume production.
What is an ultrasonic insert?
An ultrasonic insert is installed using high-frequency ultrasonic vibration, which generates localised frictional heat at the insert-plastic interface. This melts a thin layer of surrounding plastic, allowing the insert to seat into the part. The plastic re-solidifies almost immediately around the insert, producing a fast, strong, and consistent installation suited to high-volume automated production.
What is a molded-in insert?
A molded-in insert is placed into the injection mold cavity before the plastic is injected, becoming permanently embedded in the part as it forms. This produces the strongest possible bond between insert and plastic, since there is no secondary installation step or localised heating. Molded-in inserts require the insert to be specified at the tooling design stage.