Abstract: A free-swinging cutter element for a timber thinning machine includes a generally stirrup-shaped member having an outer wall and integral side walls. Each half of the member is formed as the frustrum of a triangle so that bevels on the upper and lower surfaces form sharp cutting edges that incline to respective upper and lower points in the center of the outer wall. This construction moves the center of mass further outward toward the outer wall to increase chipping and cutting efficiency, which is further increased by the form of the cutting edges. A single edged cutter having similar overall shape also is provided.