The DHR171Z is a 17mm cordless Rotary Hammer powered by 18V Li-ion battery (not included) to deliver up to 1.2 Joules of impact energy and 4,800 impacts per minute.The variable speed trigger allows the operator to adjust the speed based on the material or application and the constant speed control automatically applies additional power to the motor to maintain speed under load. The brushless motor eliminates carbon brushes enabling the motor to run cooler and more efficiently for longer life and generates less heat build-up.