Embedding captive nuts in 3D printed parts
A captive nut is a simple way to add a durable metal thread to a 3D printed part. Hexagonal pockets are especially useful because they stop the nut from rotating while the screw is tightened. The important variables are pocket clearance, access and enough plastic around the nut.
Hexagonal pockets
The pocket is based on the nut's across-flats dimension. But CAD pocket = exact standard nut dimension is not automatically enough. Allow for print tolerance.
Side insertion
Advantages: simple assembly, no print pause needed. Disadvantages: opening remains visible, nut may slide out unless retained.
- Advantage: simple assembly
- Advantage: no print pause needed
- Disadvantage: opening remains visible
- Disadvantage: nut may slide out unless retained
Insert during printing
Workflow: pause print → insert nut → resume print. Advantages: completely captive nut, clean outside surface. Risks: incorrect pause height, nozzle collision, nut protrudes above the layer, unsafe pause location.
- Advantage: completely captive nut
- Advantage: clean outside surface
- Risk: incorrect pause height
- Risk: nozzle collision
- Risk: nut protrudes above the layer
- Risk: unsafe pause location
Leave enough material around the nut
A large nut pocket inside a thin wall weakens the part. Consider:
- larger boss
- more surrounding wall
- ribs
- fillets
Nut or heat-set insert?
Captive nut: inexpensive, robust, no heated installation tool. Heat-set insert: compact, cleaner integration in many designs, purpose-built for plastic. Both can be appropriate.