Power-driven knockout tools are provided, including knockout tool accessory devices for power-driven tools. A plurality of different die sets can be coupled to the knockout tools, for forming openings through rigid plate or sheet material. The knockout tool portion of the tools may include a transmission that provides for sufficient speed reduction and corresponding increase in output torque from an input speed/torque associated with a rotary force input to the transmission to an output speed and an output torque for the pulling of a punch portion of the die set through the rigid sheet or plate material.