If your part needs a screw or bolt, there are several routes to a thread. Which one you pick depends on how often the thread will be used, how much it's loaded and which material you print in. Here are the four most common methods and when each one fits.
Printed threads
You can model the thread directly in CAD and print it. This works surprisingly well for coarser threads.
- Good for: lids, jars, adjustment screws and parts rarely taken apart.
- Keep in mind: avoid threads finer than roughly M6 — smaller threads come out blurry in FDM. Vertical threads (axis pointing up) usually print most evenly.
- Limitation: plastic threads wear with repeated use and tolerate low torque.
Heat-set inserts
A brass insert that you melt into a pre-drilled hole with a soldering iron. This is often the best solution for functional parts.
- Good for: parts screwed apart and back together often, or that need to hold firmly.
- Advantage: gives a strong, metallic thread that handles both force and repetition.
- Keep in mind: design the hole to the insert's specification, usually slightly smaller than the insert's outer diameter so the plastic can flow around it.
Tapping
You print a smooth hole and cut the thread afterwards with a tap, just like in metal or wood.
- Good for: one-off parts where you don't want to buy inserts, and when the thread isn't heavily loaded.
- Keep in mind: works best in tough materials like PETG. Pre-drill the hole to the core diameter of the thread you want to cut.
- Limitation: the plastic thread is still weaker than a metal insert.
Captured nuts
You design a pocket in the part where a standard hex nut slides in, and the screw grips into it.
- Good for: robust, removable screw joints without special tools or inserts.
- Advantage: all the thread strength sits in the metal nut — cheap and reliable.
- Keep in mind: place the pocket so the nut can be inserted during printing or afterwards, and give it a little clearance so it slides in.
How to choose
- Rarely used, coarse thread → printed thread.
- Functional, repeated assembly → heat-set insert.
- One-off part, moderate load → tapping.
- Strong, removable connection → captured nut.
A good ground rule is to never make a plastic thread carry the load a metal thread can take. If the part is screwed apart again and again, or tightened with torque, a heat-set insert or a captured nut almost always wins in the long run — even if it costs a little more in material and assembly. Printed threads and tapping, on the other hand, are fast, cheap and perfectly adequate for lightly loaded joints.
The right thread starts with the right hole, so read up on tolerances and fits before you design. If you're unsure which method suits your part, upload your model for an instant quote and we'll give a recommendation.