A disk for use with a tillage machine includes a body portion rotatable about an axis of rotation. The body portion has a circumferential edge and a concavity with a first radius defined from a point on the axis of rotation. A hub portion is continuous with the body portion and presents an abutment face having a concavity with a second radius defined from a point on the axis of rotation. An aperture extends through the abutment face and is centered about the axis of rotation.