Heat-set threaded inserts for 3D printed parts

Printed threads have limits. Brass heat-set inserts give your HP Multi Jet Fusion (MJF) and FDM parts real metal threads that survive repeated assembly and clamping loads. Size your holes with the calculator below, and we’ll install the inserts.

Heat-set threaded insert hole calculator

Choose an insert

Pick a thread size and installed length to get the hole, depth, and wall to model.

Technology
Thread
Show in
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Hole Ø
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Model this diameter
Min. depth
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Blind hole
Min. wall
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Insert to any wall or edge
Min. boss Ø—
Insert OD (knurl)—
Installed length—
Manufacturer hole Ø (max.)—
McMaster-Carr P/N—
Parts with inserts are quoted manually.
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WHEN YOU NEED THEM

When 3D printed parts need threaded inserts

Threads printed directly into PA12 nylon work for parts that are assembled a few times and left alone. Clamping loads and repeated service ask more of a plastic thread than that, and below M6 (1/4 in) HP recommends inserts instead of printed threads. Anywhere a fastener carries load or has to come apart for service, the part needs metal threads.

A heat-set insert goes in hot. A soldering iron heats the knurled brass sleeve, and as it is pressed into the printed hole, the surrounding 3D printed plastic melts and flows into the knurls and undercuts. When it cools, the plastic locks around the insert mechanically.

Where they belong

  • Serviceable assemblies and enclosures — covers, lids, panels, and housings that get opened for maintenance, inspection, or access through the life of the product.
  • Clamped joints — mounting points, brackets, and frames where the fastener has to be torqued.
  • Jigs and fixtures — production tooling that is rebuilt, adjusted, and reconfigured on the floor.

How do you size a hole for a heat-set insert?

The hole is one of the most important details in how well the insert holds. Start from the insert manufacturer’s hole specification, not the nominal thread size; the calculator above gives the value to model for MJF and FDM. An oversized hole weakens the joint, and a hole that’s too small can crack the boss.

Two things to design in from the start:

  • Boss wall thickness. Leave enough material around the insert to contain it. A thin boss leaves the knurls too little plastic to grip.
  • Depth. Make the hole deeper than the insert so displaced material has somewhere to go rather than lifting the insert proud of the surface.

Printed orientation affects the finished hole.

We install heat-set threaded inserts in both MJF PA12 and FDM parts.

Hole Ø

Manufacturer hole + 0.2 mm (0.008 in) in MJF · as specified in FDM

MJF prints holes slightly smaller than modeled.

Depth

Insert length + 1 mm (0.04 in)

Wall

Boss Ø = 2 × insert OD

Tolerance

±0.25 mm (0.010 in) XY · ±0.42 mm (0.017 in) Z

MJF, features up to 30 mm (1.18 in), general dimensional profile. See PA12 nylon tolerances.

FAQ

Heat-set inserts: common questions

Yes. Your CAD file needs to include the holes, sized for the insert you plan to use. We print the part as designed and don't add or resize holes. Parts with inserts are quoted manually: send us the insert positions, size, and quantity, and drawings if you have them.

Pull-out strength comes down to the hole and the material around it. A correctly sized hole and a full boss give the knurls the most plastic to lock into, and that's what holds the insert against pull-out and torque.

Yes. Inserts go in after finishing, so dye and coatings are applied to the part first.

No, and it isn't meant to be. The values it returns are a well-grounded starting point, not a final dimension. The geometry and the mass of material surrounding each insert affect how the plastic flows and holds, and the same thread size can behave differently in a thin boss than in a solid block. Before a production run, send us your CAD files with the hole stepped in small increments, and a few prototypes will show which size holds best in your part.

Send us the file

Upload your file for a 3D printing quote, or tell us what your parts need to do.

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