A rotary impact tool comprising: a housing; an electric motor supported in the housing; a drive assembly for converting a continuous torque input from the motor to consecutive rotational impacts upon a workpiece of at least 1220 Nm (900 ft-lbs) of fastening torque, the drive assembly including an anvil (34, 212) having a bore (132, 216) in a distal end thereof for receipt of the workpiece or a tool bit for performing work on the workpiece, the bore defining a hexagonal cross-sectional shape in a plane oriented transverse to a rotational axis of the anvil, the bore having a nominal width of 1.111cm (7/16 inches), a hammer that is both rotationally and axially movable relative to the anvil for imparting the consecutive rotational impacts upon the anvil, and a spring for biasing the hammer in an axial direction toward the anvil; a battery pack supported by the housing for providing power to the motor, the battery pack having a nominal voltage of at least 18 Volts and a nominal capacity of at least 5 Ah; wherein the rotary impact tool has an overall weight including the battery pack that is less than or equal to 3.4kg (7.5 lbs), and wherein a ratio of the fastening torque to the overall weight is greater than or equal to 360 Nm per kg (120 ft-lbs per pound), wherein a mechanism efficiency of the rotary impact tool is defined as: η a = BPM × KE Hammer, Drilling Voltage motor × Current motor, wherein BPM is the number of impacts per minute, KE Hammer, Drilling is a kinetic energy of the hammer during a loaded condition and prior to impact with the anvil, Voltage motor is a voltage across the motor, and Current motor is a current drawn by the motor, wherein a first performance ratio (PR 1) of the rotary impact tool is defined as: PR 1 = η a Inertia hammer × 1 216,000, wherein Inertia hammer is a moment of inertia of the hammer, and wherein the first performance ratio of the rotary impact tool is greater than 1. a housing; an electric motor supported in the housing; a drive assembly for converting a continuous torque input from the motor to consecutive rotational impacts upon a workpiece of at least 1220 Nm (900 ft-lbs) of fastening torque, the drive assembly including an anvil (34, 212) having a bore (132, 216) in a distal end thereof for receipt of the workpiece or a tool bit for performing work on the workpiece, the bore defining a hexagonal cross-sectional shape in a plane oriented transverse to a rotational axis of the anvil, the bore having a nominal width of 1.111cm (7/16 inches), a hammer that is both rotationally and axially movable relative to the anvil for imparting the consecutive rotational impacts upon the anvil, and a spring for biasing the hammer in an axial direction toward the anvil; an anvil (34, 212) having a bore (132, 216) in a distal end thereof for receipt of the workpiece or a tool bit for performing work on the workpiece, the bore defining a hexagonal cross-sectional shape in a plane oriented transverse to a rotational axis of the anvil, the bore having a nominal width of 1.111cm (7/16 inches), a hammer that is both rotationally and axially movable relative to the anvil for imparting the consecutive rotational impacts upon the anvil, and a spring for biasing the hammer in an axial direction toward the anvil; a battery pack supported by the housing for providing power to the motor, the battery pack having a nominal voltage of at least 18 Volts and a nominal capacity of at least 5 Ah; wherein the rotary impact tool has an overall weight including the battery pack that is less than or equal to 3.4kg (7.5 lbs), and wherein a ratio of the fastening torque to the overall weight is greater than or equal to 360 Nm per kg (120 ft-lbs per pound), wherein a mechanism efficiency of the rotary impact tool is defined as: η a = BPM × KE Hammer, Drilling Voltage motor × Current motor, wherein BPM is the number of impacts per minute, KE Hammer, Drilling is a kinetic energy of the hammer during a loaded condition and prior to impact with the anvil, Voltage motor is a voltage across the motor, and Current motor is a current drawn by the motor, wherein a first performance ratio (PR 1) of the rotary impact tool is defined as: PR 1 = η a Inertia hammer × 1 216,000, wherein Inertia hammer is a moment of inertia of the hammer, and wherein the first performance ratio of the rotary impact tool is greater than 1. wherein BPM is the number of impacts per minute, KE Hammer, Drilling is a kinetic energy of the hammer during a loaded condition and prior to impact with the anvil, Voltage motor is a voltage across the motor, and Current motor is a current drawn by the motor, wherein a first performance ratio (PR 1) of the rotary impact tool is defined as: PR 1 = η a Inertia hammer × 1 216,000, wherein Inertia hammer is a moment of inertia of the hammer, and wherein the first performance ratio of the rotary impact tool is greater than 1. wherein Inertia hammer is a moment of inertia of the hammer, and wherein the first performance ratio of the rotary impact tool is greater than 1.