It has 2 main functions
Firstly,Prevent debris from bouncing up and Prevent damage to the lens.
Secondly,Help control the area and size of the auxiliary gas diffusion.
About the spray nozzle,It has single spray nozzle and double spray nozzle.
Double spray nozzle mainly used for cutting carbon steel, other kinds of material mainly use single spray nozzle.
So it not the same.There are mainly 3 diameter of nozzles, 1.5mm , 2.0mm, 3.0mm.