Abstract: An improved design for a cage mill for disintegrating or reducing materials such as ore, grain, etc., consisting of a movable and a stationary portion for housing two cooperative rotatable cage assemblies mounted on coaxial shafts, and each having two rows of impact members alternating with those of the other cage assembly. The axial length of the impact members increases radially outwardly from the axis of the two shafts, and a disk for each cage assembly has a stepped portion for mounting the longer row of impact members and the ends of the members are protected by impact rings. The stepped portion provides an offset area for nesting the ring of a preceding row to protect the ring against abrasion. For each cage assembly a tapered split ring nut arrangement at the end of the shaft forces the cage against a hub rigidly secured to the shaft, and a locking means secures the nut to the shaft.