Almost every printer sold arrives with this nozzle, and almost every piece of printing advice on the internet was written by someone using one. That second fact is more important than any of its physical properties, and it is the reason this size deserves a page of its own rather than a line in a table.
The default's own figures
| Figure | Value |
|---|---|
| Diameter | 0.4 mm |
| Practical maximum layer height | 0.3 mm |
| Typical extrusion width | 0.45 mm |
| Realistic volumetric flow | 8–25 mm³/s |
That flow range is wide because it is not really a property of the nozzle. A short melt zone on an older machine will manage the bottom of it; a high-flow hotend on a modern one will exceed the top. The hotend is the variable and the nozzle is the constant, which is the single most useful thing to understand about flow figures anywhere on this site.
Why the default status matters more than the dimensions
When you read that a certain temperature cures stringing, that a certain wall count gives a certain strength, or that a certain speed is achievable, the person writing it had a 0.4 mm nozzle fitted. Fit something else and a proportion of that advice silently stops applying:
- Wall thickness recommendations assume 0.45 mm lines. "Three walls" means something different at 0.68 mm.
- Retraction settings assume this orifice's pressure behaviour.
- Speed settings assume this flow demand. The same speed through a 0.6 mm nozzle asks for roughly twice the flow.
- Support settings — separation distances and interface layers — are tuned around this line width.
None of that is a reason to keep the default. It is a reason to know that when you change nozzle you have moved outside the profile everyone else is describing, and that unexpected results are more likely to be the nozzle than the machine.
The compromise, and why it was well chosen
It is a good one. A 0.45 mm line resolves detail down to about a millimetre convincingly, bridges reliably, produces clean overhangs with ordinary cooling, and moves enough plastic that functional parts do not take all day.
It also handles the widest range of materials without special attention. PLA, PETG, ABS, TPU and most filled variants all print through it, though filled materials need the nozzle itself to be hardened rather than brass.
Where it stops being right
Large functional parts. A part that takes four hours here can take under two on a 0.6 mm, because both the line width and the usable layer height increase together.
Sub-millimetre features. Text below roughly 3 mm cap height, fine surface texture and delicate lattices all want 0.25 mm or finer.
Very abrasive filaments at volume. Filled materials wear any nozzle; a wider orifice tolerates the resulting wear better because a given amount of erosion is a smaller proportion of the opening.
Brass, hardened, and the wear that is not a failure
The nozzle your printer came with is almost certainly brass, which is soft, conducts heat well and machines to a good finish. It is an excellent material until you print something abrasive through it.
The important thing about nozzle wear is that it does not fail, it drifts. A worn orifice is wider than it was, so every extrusion is slightly wider than the slicer believes, and the symptom is inconsistent extrusion width or dimensions that no longer match a calibration you did months ago. Nothing announces itself.
If you print filled filament, fit a hardened nozzle before the first spool rather than after. If you print plain PLA and PETG, brass will last for years.
Keeping it as your baseline
The most practical advice about this size is procedural rather than technical: keep a working 0.4 mm profile you trust, and return to it when diagnosing anything. When a print goes wrong on an unusual nozzle, swapping back to the default separates "this machine has a problem" from "this profile has a problem", and that distinction saves more time than any single setting.
For what the alternatives change, the other sizes each have their own page — 0.2, 0.25, 0.6, 0.8 and 1.0 mm.