Nozzle diameter

Nozzle diameter is the size of the small opening at the tip of the hotend that molten filament is pushed through, most commonly 0.4mm on stock FDM printers, though smaller and larger sizes are widely available. This single measurement affects several things at once: how fast a printer can lay down plastic, how fine a detail it can resolve, and how thin a single printed wall can be.

A smaller nozzle, such as 0.2mm, can resolve finer detail and thinner walls but prints much more slowly and clogs more easily with anything less than very clean filament. A larger nozzle, such as 0.6mm or 0.8mm, moves plastic much faster and is popular for large functional prints where fine surface detail matters less than finishing quickly and printing strong, thick layers.

Nozzle diameter also interacts directly with layer height, since a very tall layer through a small nozzle extrudes poorly, and abrasive filaments wear a soft brass nozzle's diameter wider over time regardless of size. A common mistake is switching to a larger nozzle for speed without adjusting layer height and flow settings to match, which produces under-extruded, weak-looking prints.