A screening disk for use on a roller of a roller screen for screening an ore feed is disclosed, which includes first and second opposing side working surfaces, and provisions for mounting the screening disk on a shaft of the roller. At least one of the first and second side working surfaces has a plurality of protrusions operable to extend outwardly into an interstice between the applicable side working surface and a side working surface of an adjacent mounted screening disk. A spacer may be disposed in the one interstice for confining an extent of the one interstice to a region disposed generally between the third working surface and the shaft. A screening disk may have a keyway configured to receive a key for coupling the body of the screening disk to the shaft for rotation therewith.