In any drive head, there is a tradeoff between torque (power) and speed (revolutions per minute). The high torque head provides a large amount of torque (power) to the auger at a slower speed. The high torque (power) translates into the Mt-55's capability to dig 30" holes up to 5' deep in clay, gravel, sandstone and many other conditions where lower torque heads get stuck. We carry 6", 9", 12", 18" and 30" bits. Please call for pricing and availability.