The various embodiments disclosed and pictured illustrate a hammer for comminuting various materials. The embodiments pictured and described herein are primarily for use with a rotatable hammermill assembly. The double end hammer includes a connection portion having a slot therein and two contact ends for delivery of energy to the material to be comminuted. The contact ends may be formed with a cavity therein. The contact ends may also be formed with an angle on the contact end periphery. The cavity and/or the angle on the contact end periphery may be used with hammers other than the double end hammers.