Threaded Inserts For Plastic Selection Guide | Hebei Wotu Fastener Manufacturing Co., Ltd.
Threaded inserts for plastic create a reusable metal thread in a molded, printed, or machined plastic part. The main decision is not only the thread size; it is how the insert will be installed, how much load the plastic can support, and whether the joint must survive repeated assembly.
For a stable purchase decision, match the insert style to the plastic material, boss design, installation method, and service conditions before confirming quantity or price.
Brand: Wotu Surface: color zinc plated electroplating Specifications: in stock 3.5/4.0/4.5/5.0 regular wire diameter, rod length 16～80mm full range of specifications in stock, supports nonstandard length customization Packaging: 25kg cartons, whole wooden pallets
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Brand: Hengzuan Surface: blue and white zinc plated Specifications: in stock ST4.2/ST4.8full range of specifications, length 13~50mm in stock, support nonstandard length customization Packaging: 25kg cartons, solid wood packaging, support neutral packaging, private-label customization
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Brand: Hengzuan Surface: blue and white zinc plated, can be customized color zinc plated, black oxide plated Specifications: Comply with GB/T15856.2 Chinese national standard, in stock ST3.5/ST4.2/ST4.8/ST5.5 mainstream wire diameter, rod length 13mm~50mm full range of specifications, nonstandard length customization on demand, drilling applicable plate thickness 2~5mm Packaging: 25kg export cartons, full pallets wrapped with film, supports neutral export packaging, private-label customization
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Brand: Hengzuan Surface: Color zinc plated, optional blue-white zinc plated, black oxide treatment Specifications: Chinese national standard ST4.2/ST4.8/ST5.5 specifications, rod length 13~50mm in stock, supports nonstandard length customization Packaging: 25kg export cartons, full wooden pallets wrapped with film, supports neutral packaging, private-label customization
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Brand: Hengzuan Surface: blue and white zinc plated, can be customized color zinc plated, black oxide plated Specifications: Comply with GB/T15856.2-2002 Chinese national standard, in stock ST4.2/ST4.8/ST5.5 full range of specifications, length 13mm~75mm optional, supports customized nonstandard rod lengths; drilling adaptation plate thickness 0.7~6mm Packaging: 25kg export cartons, full pallets wrapped with film, supports neutral export packaging, customer private-label customization
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Brand: Hengzuan Surface: blue and white zinc plated, optional color zinc plated, black oxide treatment Specifications: Follow GB/T846-1985 Chinese national standard, in stock ST4.2/ST4.8/ST5.5 full range of specifications Packaging: 25kg export cartons, full pallets wrapped with film, supports neutral export packaging, private-label customization
Read MoreInsert selection
Compare threaded inserts for plastic by installation method, external knurl or retention profile, thread size, body length, flange style, material, and compatibility with the plastic part design. The right choice should fit both the assembly requirement and the way the insert will be installed in production.
| Criterion | What To Check | Why It Matters | Buyer Tip |
|---|---|---|---|
| Insert installation method | Compare heat-set, ultrasonic, press-fit, and self-tapping designs against the plastic part and assembly equipment. | The installation method affects cycle time, equipment needs, hole design, and the risk of cracking or distortion. | Ask which insert types are available for your plastic grade and whether installation guidance or process samples can be provided. |
| Plastic grade and part geometry | Share the resin, filler content, wall thickness, boss shape, and available installation-hole dimensions for review. | A design that works in a tough reinforced plastic may damage a thin or brittle boss, while the wrong hole fit can reduce retention. | Send a part drawing or representative sample and ask for the recommended hole and boss design. |
| Internal thread and engagement | Confirm the thread form, nominal size, usable thread depth, and screw engagement required by the joint. | Insufficient engagement can strip the insert or screw thread; excessive screw length can bottom out or damage the plastic part. | Provide the mating screw specification and clamped-part thickness before finalizing the insert length. |
| Insert material and service environment | Verify the insert material and finish against moisture, chemicals, temperature changes, and contact with the mating fastener. | The surrounding plastic may tolerate the environment while the insert or screw interface corrodes, binds, or loses serviceability. | Describe the exposure conditions and ask which material and finish are suitable for the intended service life. |
| Retention and assembly performance | Request applicable pull-out, push-out, and torque information for the chosen insert, plastic, hole design, and installation process. | Retention depends on the complete joint rather than the insert alone, so catalogue fit does not guarantee reliable assembly. | Ask how test conditions match your part and whether sample testing can confirm installation torque and repeated screw removal. |
The most important distinction is between inserts that are installed with heat, ultrasonic energy, press-fit force, expansion, or molding-in during part production. Heat-set and ultrasonic inserts are common for thermoplastics because the surrounding plastic flows around the knurl pattern. Press-fit or expansion styles can be useful when heat is not suitable, but they depend heavily on hole control and plastic strength.
This matters because the wrong installation method can damage the boss, reduce pull-out resistance, or create weak threads even if the insert material and thread size look correct on a drawing. A small change in hole diameter, boss wall thickness, or knurl geometry can change the result more than buyers expect.
Start with the plastic and production process. ABS, PC, PA, POM, PP, and glass-filled materials behave differently during insertion and loading. A brittle or highly filled plastic may need a different outside profile than a softer thermoplastic. If the part is 3D printed, tell the supplier the print material, print direction, and whether the insert will be installed after printing.
Choose the insert style around the load case. Pull-out load, torque resistance, vibration, repeated screw removal, and clamp force do not all favor the same design. Straight knurls, helical knurls, undercuts, flanges, and closed-end bodies each solve different problems. A flange can help control seating, while a blind or closed-end insert can help where screw depth must be limited.
Do not freeze the insert before checking the mating part design. Boss outside diameter, hole depth, lead-in, wall thickness, and screw engagement length should work together. A common mistake is selecting an insert from thread size alone, then discovering that the plastic boss is too thin or the screw bottoms out before clamping the assembly.
For the next step, send the thread size, insert type if already chosen, plastic material, hole or boss drawing, installation method, expected screw removal frequency, and any surface finish or material preference. If you are asking Hebei Wotu Fastener Manufacturing Co., Ltd. for supply, confirm whether the required insert style and material are available before treating the design as final.
| Criteria | Importance | Description | Example Options |
|---|---|---|---|
| Installation method | Usually the first decision after material | Heat-set, ultrasonic, press-fit, expansion, and molded-in inserts place different demands on equipment, hole tolerance, and plastic behavior. | A thermoplastic housing may suit heat insertion, while a part that cannot be heated may need a mechanical press-fit or expansion style. |
| Plastic material and boss design | Critical for retention and crack resistance | The surrounding plastic must support installation force and service load. Boss diameter, wall thickness, hole depth, and bottom clearance can change performance more than the thread size alone. | A thin boss around a long insert may crack during installation or under screw tightening. |
| Retention profile | Important when load or screw cycling is significant | Knurls, grooves, undercuts, and flanges affect pull-out resistance, torque resistance, seating control, and resistance to rotation. | A flanged insert can help control seating depth, while a more aggressive external profile may improve resistance to turning in the plastic. |
| Open-end versus closed-end body | Application-dependent | Open-end inserts allow screw length flexibility but need enough clearance behind the insert. Closed-end or blind styles help limit screw depth or protect the opposite side of the part. | A cover with limited internal clearance may require a closed-end insert to prevent the screw from passing through. |
| Assembly service life | High for parts opened repeatedly | Parts that are serviced often need stable metal threads, controlled clamp load, and enough engagement length to avoid loosening or stripping the plastic support. | An electronics enclosure opened for maintenance needs more attention to screw cycling than a one-time assembled trim part. |
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No. Softer thermoplastics, brittle plastics, and glass-filled materials respond differently to heat, pressure, and loading. Confirm the resin grade, filler content if known, and molded or printed part design before fixing the insert style.
Heat-set inserts often suit thermoplastics because heat allows the plastic to flow around the external profile. Press-fit inserts avoid heat but need tighter hole control and enough plastic strength around the boss. The better choice depends on the material, available installation equipment, production volume, and required pull-out or torque resistance.
Thread size is only one part of the decision. Body length, outside diameter, knurl pattern, flange style, hole depth, boss wall thickness, and screw engagement can all affect whether the joint works reliably.
A frequent mistake is leaving too little plastic around the insert. Even a strong metal thread can fail if the boss cracks, deforms, or cannot support the installation force. Check the boss diameter, wall thickness, lead-in, and bottom clearance together with the insert drawing.
A molded-in insert can be useful when the part is designed around insert placement during molding and the assembly needs strong retention without a secondary installation step. It also adds tooling and process considerations, so it is not always practical for prototypes, small batches, or designs that may still change.
Send the internal thread size, target insert length if known, plastic material, installation method, hole or boss dimensions, expected screw cycles, and the load direction. If the style is not decided, share the part drawing and assembly requirement so suitable options can be discussed.
Send the thread size, plastic material, installation method, and a drawing or hole dimensions. Also note the expected load or service frequency so the insert style can be checked against the application.
