Abstract: A screen intended for screening pulp chips or equivalent, wherein two or more screen baskets are fitted one above the other. At least one of these baskets consists of two or more screw spirals journalled to the screen basket, the spiral wings of said spirals being fitted as interlocking in between each other. The outer circumference of each wing extends to the proximity of the mantle face of the core part of the adjoining spiral. The adjoining spirals are opposite-handed and have opposite directions of rotation, their rotation being synchronized in relation to each other, and the distance of the interlocking parts of the wings from each other corresponds to the maximum acceptable thickness of the chips.Two screen baskets fitted one above the other are supported by the frame, and they are connected to each other by units that permit free movement of vibration of one or both of the screen baskets. The movement of vibration is produced by transferring a cam shaft movement from one basket to the other.