Heat-Set Threaded Inserts (4-40 Threads)

Heat-Set Threaded Inserts (4-40 Threads)

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Heat-Set Threaded Inserts are a great option for 3D printed parts or making repairs to any thermoplastic part. They provide a much stronger connection than simply threading screws into the plastic. Brass will also last much longer than plastic threads and is less likely to cross thread which makes them ideal for parts that are assembled and disassembled often. These inserts can be easily and quickly installed by heating them with a standard soldering iron on a low-heat setting and using the soldering iron's tip to press the insert into place.  The melted plastic will flow around the knurls and ridges on the insert as it is pressed in and solidify when cool, locking it in place. These inserts have #4-40 SAE (Imperial)threads.

Need a different thread size? We have more inserts available here, including an assortment box with 10 different sized inserts.


Insert Specifications:

  • Maximum Insert Diameter:                  0.172" (~4.37mm)
  • Tapered End Diameter:                         0.157"(~3.99mm)
  • Overall Insert Length:                           0.135"(~3.43mm) Dimension "C" below
  • Optimum Pilot Hole Size:                     0.153" (~3.89mm) Dimension "A" below
  • Optimum Surface Hole Diameter:        0.159"(~4.04mm) Dimension "B" below
  • Recommended Min Wall Thickness:    0.093"(~2.36mm)
  • Vanes:                                                     1
  • Material:                                                 Brass


Design tips for using Heat-Set threaded inserts

Ideally tapered inserts are meant to be placed into holes designed with an 8° taper. When using the inserts on 3d printed parts, we find that the gaps between the stacked layers, and the tendency of FDM style 3d printers to produce slightly undersized holes usually compensates for this if installing them in non-tapered holes. However you may have to experiment with your set-up if you need the strongest connection possible for your application. It is also recommended to leave an additional clearance of ~0.03"(~0.75mm) below the insert if using them in "blind" holes to accommodate any molten plastic that might be pushed below the insert during installation.

Heat Set Insert hole dimension guide

When fastening multiple parts together, make sure the the diameter of the screw hole on the part lying directly against the part with the heat-set insert is smaller than the outer diameter of the insert. This will ensure that the clamping force generated by tightening the screw does not pull the insert out of place.Design tips for using threaded inserts

Alternatively, you might want to consider placing the insert on the back side of the part if the screw goes completely through. Heat Set insert installation on back of through hole

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