Abstract: Materials such as wood chips are classified by thickness by feeding same through a chip outlet onto a rotating disc adjacent the axis of rotation of the disc, the disc cooperating with a housing to define a tapering passage terminating in a narrow, restricted outlet adjacent the periphery of the disc, orienting bars project from the disc and extend radially from the axis of rotation to beyond the chip inlet. A frusto conical chip orienting surface extends from the radial outward extremities of the orienting bars toward the outlet in a position traversing the path of material leaving the orienting bars.In one embodiment, an oversized outlet is provided, positioned trailing the orienting bars in the direction of rotation behind a substantially unobstructed trajectory of material leaving the orienting bars. In another embodiment, the oversized outlets are replaced by breaker bars that cooperate with cooperating breaker bars on the housing to shear positions of the material away.