As 3D printing becomes more prevalent in end-use products, engineers are pushing the limits of what components can do, seeking higher strength, better durability, and smarter integration with standard hardware. Among the most critical features are threaded connections.
At Avid Product Development, we help our clients design and manufacture functional, production-grade 3D printed parts. To evaluate the best fastening methods, we conducted a comparative study using our tensile tester.
The objective was to measure the pull-out strength of ten common fastening strategies used in 3D printed plastic parts, assess how print tolerance affects performance, and review the pros and cons of different fastening methods.
Watch our engineering team put ten common fastening methods to the test on 3D printed PA12 parts. This side-by-side comparison reveals how design choices and tolerances impact pull-out strength and durability.
Methodology
We designed a standardized test plate featuring ten fastening regions, each using an M4 fastener.
Testing was performed using a Mark-10 tensile tester with a custom screw puller held in the load cell crosshead. A metal plate was designed to hold the test plate to the base and isolate the individual thread being tested. Each fastening method was pulled to failure, and peak force readings were recorded as maximum pull-out strength.
We also printed variants of each of the ten connection types with 5% undersized and 5% oversized diameters (based on the nominal hole diameter) to study the sensitivity of printed threads and inserts to hole tolerance.
Results
The following table shows the peak force for each fastener style, as well as the variations that occur when a hole is undersized or oversized.
Key Takeaways
Hex Nut in Pocket: The Clear Strength Leader
● Achieved the highest tensile strength at 952 lbF.
● Requires backside access and takes up a significant amount of space, but is ideal for structural assemblies.
● Excellent for high-load and repeated assembly applications.
Blind Hole: Best Performer
Plastite outshines the competition as the best blind hole solution for applications that don’t require frequent screw removal and installation. The plastite also demonstrates easier installation and more tolerance forgiveness compared to its second and third place rivals (tap drill and long heat insert, respectively). The tap drill is more susceptible to cracking the part for undersized holes, and the long heat insert shows significant strength loss in the case of oversized holes.
Heat Set Inserts: Reliable and Repeatable
● Long inserts installed from the front side yielded 452 lbF.
● When installed from the back side, strength increased to 705 lbF, showing the benefit of distributing load across the full insert body.
● Short heat set inserts performed lower (244 lbF) but are sufficient for light-duty or compact designs.
● A good solution when metal threads are needed for repeated assembly and disassembly.
Thread-Forming and Self-Tapping: Convenient Options
● Plastite® screws (562 lbF) offered strong retention with simple installation.
● Tap drill holes (the hole size used prior to tapping in a standard machining operation) showed surprisingly good performance (510 lbF) but induced unnecessary stress in the part, cannot be used in areas with thin walls, and require a significant amount of torque to install.
● The self-tapping insert provided a higher level of pull-out force than the similarly sized short heat-set insert, and does not require heat to install. It also does not seem to be as sensitive to print tolerances.
Weakest Performers: Screw-to-Expand and Press-In Inserts
● Despite its self-locking design, the screw-to-expand had the lowest pull-out strength (76 lbF).
● Dependent on perfect geometry, poor interference resulted in premature failure. Oversizing the hole by 5% leads to a nearly undetectable pull-out force.
● The twist hex press in insert, while taking up a significant amount of space, has noticeably worse performance than the other insert options.
Orientation Matters
Not only did installing the tapered heat set insert from the back increase the pullout force dramatically (705 lbF vs 452 lbF). It also changed the nature of the failure. Instead of catastrophic failure, the insert slowly pulled through, retaining a significant amount of strength.
Design Recommendations
Our engineering team created the following chart to help select the right kind of insert for your nylon part, printed on an HP MJF printer. This is not an exhaustive list, and there will be exceptions, but it is meant to be a starting point to help with design decisions.
Conclusion
Inserts and fasteners in 3D printed parts are not one-size-fits-all. Performance depends heavily on the type of insert, installation method, part geometry, and material. By testing under controlled conditions, Avid Product Development provides our clients with proven, real-world data to support smarter, more reliable designs.
Whether you’re developing an end-use product or a critical assembly fixture, we can help you engineer with confidence.
Download this report as a PDF here.
