Abstract: A coaxial feeder for connection to the inlet of a disc refiner includes a channel defining means which contains a bladed screw the blade of which has a relatively short axial length and is housed to position coaxially of the discs, to which it feeds material for refining purposes, and in concentric spaced relation to the wall structure which bounds said channel. The material to be refined is introduced to the down side of the screw blade. At the outer periphery of the blade, at the lowermost limit of its travel, is a bar or plate-like control device which is substantially coextensive with the blade and arranged to specifically direct material to the space between the discs of the related refiner with minimal interference or disruption. The control device presents a surface to the material moved on the down side of the screw blade which effectively inhibits bypass of material to the upside of the blade, having regard for the direction of its rotation in use.