A 0.4mm nozzle means that the diameter of the nozzle hole is 0.4mm. Among the nozzles that spray liquid, the 0.4mm diameter spray hole can produce a mist-like spray shape, which is also called an atomizing nozzle.

The diameter of the spray hole of the nozzle has a great relationship with the particle size of the sprayed liquid. For example, when the diameter of the spray hole is less than 0.6mm, the spray form is generally mist. When the diameter of the spray hole is less than 2mm, the spray form is generally like a light rain. When the diameter of the spray hole is less than 5mm, the spray pattern is generally similar to moderate rain, and so on, the larger the spray hole diameter, the larger the spray flow rate, and the larger the spray droplet diameter.