Threaded Inserts and Fasteners for Plastics and 3D Printing | Installation Guide
Strengthening 3D Prints and Plastic Builds with Specialist Fasteners
If you've ever worked with 3D printed parts and prototypes, you know that securing and fastening together your creations can be challenging and time-consuming. Thermoplastic materials like PLA, PETG, ABS, and resin are fantastic for creativity but when you want to combine your printed components using different materials, its often confusing which fastening approach is best..
That's where threaded inserts for plastic and specialist fasteners come into their own. These simple solutions reinforce mechanical strength, allowing you to assemble and disassemble without a hitch and helping make modular designs a reality.
This installation guide will walk you through the different types of threaded inserts for 3d printed parts and their methods of installation into plastic materials, both pre and post printing as well as other fastener solutions you can utilise with your printed projects.
Contents:
Polyfix Screws: High-Performance Fastening in 3D-Printed Plastics.
What they are and how they function:
Polyfix screws specifically are engineered for secure fastening into soft or brittle plastics and other suitable materials. Their specialist thread profiles maximise grip without requiring a metal insert and allow for rapid testing/prototyping of components thanks to their ease of installation and reusability.
Polyfix Screws come in two thread profile options, the 30° variant is optimised for fine control in softer or lower-density plastics, offering a tighter, more precise grip into the material. The 45° thread is suited to, providing a deeper, more aggressive engagement suitable for harder or denser plastics. These angled thread profiles help distribute force more evenly, reducing the risk of delamination along layer lines in PLA 3D printed parts.
Benefits:
- Fast Installation – No special prep or additional components required, making them ideal for rapid prototyping and easy installation.
- Cleaner Finish – Polyfix screws offer a neat, professional result without the mess or weaknesses of adhesives or press-fit joints.
- Prevents Delamination – The angled threads on Polyfix Screws help evenly distribute force, reducing stress and the risk of delamination in printed materials like PLA.
Best Suited For:
- Best Fit For – PLA, ABS, PETG, and other thermoplastics, where quick, secure fastening is needed.
- Works Well With – Models/miniatures and cosplay props, prototypes, and projects requiring regular disassembly.
- Ideal for Robotics – Perfect for small assemblies, like AccuBots or Antweight robots, where reusability and secure fastening are essential.
Materials and Re-usability Window:
You can typically expect around 30–50 remove-and-replace cycles in resin and 10–20 in PLA before signs of fatigue appear. If your project demands higher durability or more frequent disassembly, consider switching to a brass heat-set insert or another reusable fastening method covered in this guide that better suits your material and use case.
Using Polyfix Screws With Your 3D Prints:
1) Model pilot holes directly into your 3D print to ensure proper alignment and maintain material strength during fastening. This method is especially effective when dealing with thin walls or hollow structures, where drilled holes may compromise integrity or leave too little material for the screw to grip. If you're working with a solid plastic part post-print, carefully drilling a slightly undersized pilot hole is also a suitable alternative.
2) Drive in the screw with slow, controlled torque being sure not to over-tighten the screw or push down unevenly which can create alignment issues.
3) That's it! Polyfix screws offer possibly the simplest installation method of any fastener type into 3D printed or plastic parts and possibly one of the most cost effective.
Self-Tapping Inserts: Clean Threads Without Pre-Tapping.
What They Are and How They Function:
Self-tapping inserts are metal fasteners designed to cut their own threads as they are driven into plastic or other parent materials. Unlike heat-set or press-fit inserts, they do not rely on heat or friction for retention. Instead, their external thread pattern bites directly into the parent material, forming a strong threaded-bond during installation. Choose Self-Tapping inserts when you need robust, reusable threads in plastics without pre-threading or access to thermal tools.
Benefits:
- No Need for Heat or Special Tools – Unlike heat-set inserts, self-tapping inserts do not require thermal tools, saving time and preventing any risk of material distortion during installation.
- Durable, Reusable Threads – The cutting action of self-tapping inserts creates strong, reliable threads in plastics, allowing for repeated use without degradation, unlike printed threads that can wear out.
- Ideal for Retrofit Applications – They are particularly effective for reinforcing existing holes in 3D prints or molded plastic components, providing a quick and effective upgrade for weak or stripped threads.
- High Torque and Pull-Out Resistance – The external cutting threads create a strong grip in plastic, ensuring the insert can withstand heavy loads and repeated disassembly.
Best Suited For:
- Best Fit For – Applications in PLA, ABS, Polycarbonate, and PETG, where high strength and ease of installation are needed without pre-tapping or heating.
- Works Well With – 3D printed enclosures, electronic housings, prototypes, and any plastic part that requires a secure, reusable thread but doesn’t have the time or tooling for heat-set or press-fit inserts.
- Great for Repairs – When repairing or retrofitting stripped threads, self-tapping inserts offer a quick, reliable solution that restores functionality without replacing entire parts.
How To Install Self-Tapping Inserts for Plastic:
1) Create an undersized hole in your design file or drill one into the part/assembly to house the insert. Different sized inserts require different pilot hole sizes and minimum wall thickness of the surrounding material, always check the Product Specifications.
2) Self-Tapping inserts can be installed with a number of specialist tools depending on your insert type. Here we cover a simple method of installation that required no specialist tooling. Selecting a corresponding threaded fastener, washer and nut of the same size as your insert, here we have gone with M5.
3) Assemble your threaded fastener, washer and nut together in the order shown to create your assembly tool. You only need to tighten this assembly by hand to begin with.
4) Fully thread your assembly tool into the insert. Then align the base of the insert with your pilot hole ensuring that everything is aligned correctly. If the material is suitable you may want to begin the threading process by hand.
5) Fully drive the insert into the part by turning the head of your assembly tool using the correct drive bit, the head of your insert should sit flush with the parent material once inserted. You can then remove the threaded component, washer and nut leaving the installed insert in place.
Brass Heat-Set Inserts: Strong, Reusable Threads for Repeated Use.
What They Are and How They Function:
Brass Heat-set inserts for plastic are knurled components designed to melt into 3D printed components and other suitable materials using a suitable heat source. As the plastic cools around the insert knurling, the insert locks in place. These inserts effectively create durable internal threads that allow other fasteners, such as machine screws or bolts, to repeatedly hold components together without loss in performance due to re-fastening, something printed threads can struggle with.
Benefits:
- Reusable, Strong Threads – Brass heat-set inserts create a durable, reusable thread in plastics, ideal for parts that need frequent disassembly or reassembly without sacrificing thread integrity.
- High Resistance to Pull-Out and Rotation – The knurled design of heat press inserts ensures maximum pull-out resistance and prevents rotation under load.
- Professional-Grade Finish – Once installed, brass inserts provide a clean, professional-grade finish that makes your 3D printed components look and function like a high-quality, commercial product.
Best Suited For:
- Best Fit For – PLA, PETG, ABS, and other thermoplastics, offering high strength for mechanical and structural applications, even in thin-walled or delicate parts.
- Works Well With – Robotic assemblies, swappable miniature or figure limbs (e.g., Warhammer models), custom camera mounts, and enclosures requiring secure, long-lasting fastening points.
- Ideal for High-Demand Parts – Perfect for applications where parts are subject to frequent assembly/disassembly, such as in robotics, custom builds, and product prototyping.
How To Install Brass Heat Press Threaded Inserts:
1) Create an undersized hole in your design file or drill one into the part/assembly to house the insert. Different sized inserts require different pilot hole sizes and minimum wall thickness of the surrounding material, always check the Product Specifications.
2) Position the insert above/just inside the lip of your undersized hole ensuring the alignment is correct before applying any heat or pressure.
3) Using a Heat-Press or soldering iron with the correct sized attachment. Heat the top of the insert and press down gently, you don't need much force, most of the time the weight of the press alone is enough.
4) Once the insert is in the correct position, retract the heat-press head (you might need to tap the press to release the insert) leaving the component in place.
5) Then using a scrap piece of metal, press the top of the insert flush with the surrounding material. This cools the component and ensures flush alignment with your parts.
Tip: Before attempting installation into finished parts consider installing a “Trial” Insert into some sacrificial/scrap material.
Press-Fit Inserts: Fast, Tool-Free Thread Integration.
What They Are and How They Function:
Press-fit inserts are a type of brass threaded insert that rely purely on friction to stay in place. Unlike heat-set or expansion inserts, they don't require heat or torque to install. Instead, they are pushed into a hole that has been precisely designed/drilled and using their ribbed design they mesh with the surrounding material. Once inserted, they provide durable internal threads, enabling secure fastening with screws or bolts.
Benefits:
- Fast Assembly – Press-fit inserts are quick to install, requiring no additional tools beyond a press or vice, saving time and effort.
- Tool-Free Installation – No heating or special tools needed, making them a convenient option for fast, reliable thread integration.
- No Thermal Distortion – Unlike heat-set inserts, press-fit inserts eliminate the risk of thermal distortion, ideal for sensitive materials or parts with thinner walls.
Best Suited For:
- Best Fit For – High-rigidity resins and dense filaments where a tight, secure fit is required without additional heat.
- Works Well With – Static fixtures, model elements, or applications where a flush, clean finish is essential.
- Ideal for Professional Finishes – Perfect for applications that demand high-quality, durable threading without thermal risk.
How To Install Threaded Inserts (Press Fit):
1) Drill or model a hole that matches the Base Diameter of your insert, always double check the technical specification prior to modeling. Remember modelling the file makes it simpler to add 3D print threaded inserts slots into your assemblies than drilling.
2) Align the insert with the opening ensuring it is square to the printed part, you may need to double check this before commencing the next step as alignments can shift with even small movements.
3) Press the insert into place using an arbor press if you have one available, we used a vice in our workshop which is also suitable. Avoid tilting or forcing the insert at an angle to ensure alignment.
4) Once fully seated, double-check that the insert is flush and correctly aligned to prevent cross-threading during screw engagement. Thats it!
Expansion Inserts: Locking Strength in for Reliable Thread Engagement.
What They Are and How They Function:
Expansion inserts are a unique type of threaded brass insert, designed to physically expand inside a drilled or designed hole when a screw is inserted and tightened. The internal threading of the insert forces the body to swell outward, pressing firmly against the walls of the cavity. This expansion allows the knurling on the insert to securely grip the surrounding material, providing solid, reusable threads.
Benefits:
- No Heat Installation – Expansion inserts don’t require heat or special tools, eliminating the risk of thermal distortion during installation.
- Minimal Wall Thickness – These inserts work effectively in thinner-walled components, offering flexibility in compact designs.
- Enhanced Pull-Out Resistance – The expansion mechanism ensures a tight, secure fit that withstands axial loads better than press-fit inserts.
Best Suited For:
- Best Fit For – Mechanical fixtures in PETG, resin, and printed resins where secure, reusable threads are required without heating.
- Works Well With – Large-scale 3D-printed dioramas or other applications where heat press tools can’t be used or access is limited.
How To Install Expansion Brass Inserts for 3D Printed Parts:
1) Drill or model a pilot hole in your part corresponding to the dimensions provided in the inserts technical specifications. You can find the details on the M5 Expansion-Fix Insert product page for the example we have here.
2) Press the Expansion Insert into the hole by hand, ensuring it is flush and seated squarely. Use light pressure to start but avoid forcing it if resistance is too high, you should be able to fully insert the insert to its complete depth. (if you encounter high resistance consider making your pilot hole larger).
3) Before you begin ensure your components threads are aligned correctly. Slowly drive in the corresponding screw or bolt to the insert size when connecting your finished parts.
As the fastener is tightened, the insert expands internally, anchoring itself against the cavity walls. Use slow, controlled torque to avoid cross threading between components. If you find it difficult to turn the screw then the pilot hole is probably too small.
Captive Nuts: For Embedded Strength in Custom-Designed Housings.
What They Are and How They Function:
Captive nuts are standard hexagonal nuts embedded into a purpose-designed cavity or housing within a 3D-printed part. As a bolt or screw is threaded in, the nut resists turning thanks to the surrounding housing creating a solid grip, almost as if the print itself is holding the nut in place like a spanner would!
Heat-Set vs Captive Nut?
Heat-set Brass Inserts excel when wall material thickness is limited, Captive Nuts shine when the housing for the nut can be deeper and you need maximum torque at hobby-budget cost. You can also design your Captive Nut sockets to include space for a washer, further increasing their performance and load distribution on tightening.
Captive Nut Benefits:
- High Torque Resistance – Captive nuts provide excellent resistance to high torque, ensuring secure connections in structural components.
- Concealed Fastening – The nut remains hidden within the housing, offering a clean and professional finish.
- Ideal for Structural Connections – Perfect for strong, permanent connections in applications requiring high mechanical strength.
Best Suited For:
- Best Fit For – Robotics frames, faceplates, and other structural components requiring high torque.
- Works Well With – Hinged panels, modular builds, and removable models (such as miniature/Warhammer bases) where concealed fastening is preferred.
Installing Captive Nuts in 3D Prints:
1) Design a hexagonal cavity in your 3D model ensuring the cavity is approximately 0.1mm to 0.2mm (PLA) or 0.15mm (Resin) larger than the nut's outer dimensions to allow for secure placement. There are numerous sizes and types of nut so ensure you have the correct component dimensions.
2) Drop in the nut post-print or to insert the captive nut mid-print (FDM Only):
- Pause the print at Z once the printer has printed the final vertical slice of the cavity for your nut.
- Then fit the nut into the hex cavity and resume the print from the same position.
3) For added security, use a small amount of adhesive to fix the nut in place prior to installing the bolt/screw. This can be superglue or more purpose suited adhesives like epoxy.
4) Secure the bolt/screw into the assembly as standard, be sure not to over-tighten your assembly (the level of force you can apply will vary depending on the type of plastic used).
Threaded Components: Bolts & Screws for Direct 3D-Printed Threads.
What They Are and How They Function:
Directly printing physical threads onto your components and parts is an attractive approach due to its simplicity and speed of installation, however it demands a high degree of accuracy both in the design of your parts and the actual printing itself. For parts not requiring frequent access or subject to strong forces, printed threads offer a perfect solution.
Benefits:
- No Additional Hardware – Directly printing threads eliminates the need for extra fasteners, making it ideal for quick, low-cost builds.
- Quick Prototyping – Ideal for rapid prototyping, allowing fast iteration without the need for complex assembly.
- Cost-Effective for Light-Duty Joints – Great for non-load-bearing applications, where cost savings are a priority and minimal fastening strength is needed.
Best Suited For:
- Best Fit For – Low-stress prototypes, enclosures, and cosmetic components that don’t require heavy-duty fastening.
- Works Well With – Alignment features in large models, hobby builds, or decorative props where strength is less critical.
Considerations when designing your threads:
Pitch choice: Coarser thread pitches tolerate FDM layer steps far better than ISO-fine, keep this in mind when selecting which components to use with your prints, you will need to plan this early on.
For Resin printers you may use coarse or fine thread pitches however there is a limit, threads finer than 0.5mm are typically too delicate or become fused after part curing, as such we recommend using alternate fastening solutions where you need a thread this fine.
Tolerance correction: Due to over-extrusion/bulging found in FDM printers you might need to allow -0.05mm additional radial tolerance for standard 0.4mm nozzles. We would always recommend printing a test thread first prior to printing a full component to ensure you have the right settings.
Resin printers are precise enough with correct calibration that you typically don't need to undersize your internal threads like we find with FDM. We do however recommend you test print a threaded section prototype before a full component to avoid wasting material when checking what threads to use.
For full technical details on Metric Thread dimensions and pitches, see our helpful printable charts:
Installing Fasteners Into Your 3D Printed Threads:
1) Select a bolt/screw that matches your project requirements and ensure you have the thread profile details. Consider the placement of the part when selecting, do you need a flush finish?
2) Use precise modelling and slicing settings to maintain accurate thread profiles. Ensure you do not alter scale settings once the part is set to print as this will alter your printed thread dimensions.
3) Install the fastener as standard, Avoid overtightening to reduce strip risk, be mindful that your connection is only as strong as the material your threads are printed into - if you need higher strength consider another fastening solution from this article.
Wrap-Up & FAQ's.
Fasteners transform how you build with plastic. They turn fragile, one-use joints into durable, modular assemblies. Whether you’re prototyping, iterating, or assembling final parts, these components provide cleaner finishes, stronger connections, and easier disassembly.
Instead of relying on brittle threads or permanent adhesives, inserts and specialist screws give you mechanical precision where it counts. They let you reinforce key stress points, integrate metal threads, and upgrade your build quality without redesigning the entire part.
For anyone working with 3D prints, they’re not just accessories- they’re transformative components every engineer should have.
Further Reading:
HowTo Measure A Screw - Now you know how to use our components discover how to select the right ones!
Imperial Thread Chards - Handy when desgining your own 3D printed threads for imperial components.
How To Make A Combat Robot - Discover our guide on how to build antweight robots, and see these powerful inserts put to use!
FAQs
Q: What are threaded inserts for plastic?
A: Threaded inserts for plastic are small threaded bushings (often metal, like brass) that you can embed into a plastic part to create a durable, reusable screw thread. They let you add strong machine-quality threads to plastic parts that might otherwise strip out or be too thin/weak for standard threads from screws and bolts.
Q: Why use threaded inserts in 3D printing?
A: They give your 3D printed parts much stronger and longer-lasting threads for bolts or screws than plastic alone. In practice, inserts allow higher tightening force and withstand repeated assembly without the threads wearing out, which is great for enclosures or parts that you need to take apart often.
Q: Are threaded inserts more reliable than printed threads?
A: Yes – a Brass Insert for plastic is generally much more reliable than directly printed threads into the parent material. Printed plastic or resin threads tend to wear out or strip after a number of uses, whereas brass inserts provide solid metal threads that hold up to stress and repeated use.
Q: Which plastics work best with threaded inserts?
A: Most common 3D printing thermoplastics can use inserts, but tougher, heat-resistant ones like ABS, PETG, polycarbonate, or nylon tend to give the best results from a performance perspective. If you’re looking for a low budget prototyping option then PLA is also a fantastic choice thanks to its flexibility with 3D printing. Remember to select the material that's right for your project.
Q: Can you put threaded inserts in PLA?
A: Yes – it’s a common practice to use heat-set inserts in PLA prints. You just have to be gentle with the heat (around 220–230 °C for the iron) so the insert melts in without warping the surrounding PLA.
Q: What size hole do I need for an M3 heat-set insert in PLA?
A: For a standard M3 brass heat-set insert, a hole 4.2mm in diameter (and 6mm deep) is ideal, remember to always check the product specification. This size gives a snug fit so when you heat the insert, it melts into the PLA and stays firmly anchored. Helpfully we have component drawings and models available for all of our inserts so be sure to check in your modeling software prior to printing!
Q: How do you install threaded screw inserts without melting the plastic?
A: You can use press-fit or self-tapping inserts instead of heat-set inserts to avoid melting the plastic. These are designed to be pushed or screwed into a properly sized hole (often with knurling or threads on the outside), and they hold in place by friction or by cutting their own threads, especially if you also add a touch of glue for security.
Q: Do threaded inserts work in resin prints?
A: Yes, you can use inserts in resin (SLA/DLP) prints, but you generally can’t heat-set them because resin won’t soften with heat. Instead, you’d use a self-tapping insert or an expanding insert – basically, a cold installation since resin prints are thermoset and need a press-in or glued insert rather than a melted-in one.
Q: What is the difference between heat-set and press-fit inserts?
A: Heat-set inserts are installed by heating the insert (with a Heat-Press or Ultrasonic Tool) so that it melts into the plastic; once the plastic cools, the insert is locked in place for a very strong bond. Press-fit inserts (also called Push-In or Cold Inserts) are not heated – you simply press or tap them into a slightly undersized hole, and they hold by friction and their knurled surface biting into the plastic.