Screening is one of the most important methods of sizing and classifying materials in a process flow sheet. Applications for screening include; sizing, pre-wetting (for example, ahead of a dense media circuit), de-watering or de-sliming. Most screening is done on materials larger than 500 µm is size because of blockage by retained particles (pegging) and because of reduced screening efficiency with fineness of particles.

There are many different types of screens available, but most work on the probability that a particle will pass through an aperture of larger dimension than the particle. For a screen to work efficiently it must present particles with dimensions smaller than the screen aperture with as many opportunities as possible to pass through the screen.