Nozzles are found on the Laser head on the fibre laser. There are 2 parameters you must look at when purchasing a nozzle; the layer and the caliber.

General rule for selecting the Caliber:

General rule for selecting the Layer:

*These rules are used as a guide only. Individual results may vary.

REASONING:
Nozzle's come in either single or double layers. The layer is in reference to what gas you will primarily be using to perform the cut; Air, Oxygen or Nitrogen. The gas you are using is dependant on what type of metal you look to cut.

When using Air or Nitrogen you would commonly use a single layer nozzle.
However, when using Oxygen as your primary gas you would use a double layer nozzle. 

The Nozzle's caliber directly effects the gas flow velocity. Smaller diameter's will result in a higher gas flow velocity which will reduce the level of molten debris. Larger Diameters will result in a lower gas flow velocity but is less effective at removing molten debris.