Heat-set inserts: a strong thread in a printed part

What it is and why it is used

A threaded insert is a metal insert with a thread for soft material. A heat-set one is fitted with heat: the insert is warmed with a soldering iron and pressed into a smaller hole. The plastic flows into the grooves on its surface and, once cooled, holds it against pulling out and turning.

A printed thread wears out with repeated screwing, a brass insert lasts hundreds of turns. That is why it suits parts that are taken apart, such as covers, holders or instrument enclosures.

How to design the hole

• Diameter. Slightly smaller than the outer diameter of the insert. The exact value is given by the insert maker, and you often fine-tune the hole by testing.
• Depth. A little more than the length of the insert, so the melted plastic has somewhere to collect.
• Wall around it. At least 1.5 to 2 mm of plastic around it, otherwise the part splits when the insert is fitted. See wall thickness.
• Entry. Add a small chamfer at the entrance of the hole, so the insert is guided better.

Material and strength

Heat-set inserts hold in both PLA and PETG. PETG tolerates more heat. PLA softens at around 60 °C, so be careful with a hot insert, see glass transition.

For a stronger hold, choose a stronger infill or more walls around the insert.

What we do and do not do

We do not fit or supply inserts. We print the part with the holes you design, and you fit the inserts yourself.

For a first batch, test the hole on one piece with your own inserts and only then order a larger number.