Abstract: In screening apparatus for paper fiber stock of the type wherein a cylindrical perforate screen member defines screening and accepts chamber on the inner and outer sides thereof in a closed housing, the inlet chamber for stock to be screened is located below the screening chamber, and the reject chamber for accumulating reject material is located above the screening chamber. Provision is made for retaining high specific gravity materials within the inlet chamber and for trapping and removing them therefrom without ever reaching the screen chamber. In addition, provision is made for developing centrifugal force effective to concentrate low specific gravity materials, such as bits of plastic foam, in the central part of the reject chamber, and a discharge outlet from the reject chamber located generally centrally of its top wall assures elimination of such light reject materials.