produce a narrow annular opening that all pulp must pass through before entering the screening zone this protects the delicate screen plate located in the screening zone from abrasion and damage due to hard oversized contaminants the term u201c oversize u201d refers to a comparison of any contaminant particle 39 s minimum dimension to the width of the apertures in the screen cylinder a particle that is said to be oversized can not fit through any of the screen apertures no matter how the particle is orientated therefore the screen cylinder retains oversize contaminants but allows undersize contaminants and other undersize materials like pulp fibers to pass through the cylinder all oversize materials are contaminants but undersize materials can be contaminants or they can be desirable materials like fibers typical pulp fibres have a minimum thickness range of 0 01 mm to 0 065 mm the slot aperture widths of the screen cylinders in the tcms will typically range from 0 1 mm to 0 25 mm these measurements indicate that no matter what type of wood fiber is screened and what screen cylinder slot aperture is chosen fibre will always be able to pass through the screen plate the size of contaminant particles found in a pulp will range from mill to mill contaminant particles that cannot pass the narrow annular opening 122 must have all dimensions greater than the distance between the rotor cap 110 and the screen retaining housing 111 in the event that a higher pulp flow rate through the tcms is required the annular opening distance could be increased conversely if a lower.