The New ARI12094B from Acdelco just arrived 

Model Number ARI2094B
Voltage 18 VDC
Drive 1/2'' Square
Max Reverse Torque 400 Nm (300 ft-lbs)
Max. Tightening Torque 640 Nm (480 ft-lbs)
No Load Speed 0-2,000 RPM
Impacts per Minute 0-3,000 IPM
Tool Weight 1.50 kg (3.30 lbs

Durable Metal Gearbox Housing
Pro-Grade Impact Mechanism
Incorporate Super Bright LED
Convenient Illumination of Work Area
Battery Indicator
Battery capacity display
4 Pole high torque motor
Soft Grip
Anti-slip and Fatigue-free

AcDelco tools are top quality tools well balanced and soft grip make these tools comfortable to use 8 hours a day, all the batteries have a charge time of 20 minutes each tool comes with 2 batteries.

This high powered wrench can remove wheel nuts from passenger vehicles and is ideal for road side and normal workshop use.

Can be used as a drill and high powered screw driver if used with our 1/2 drive converter £12 

In the construction industry this powerful tool is ideal for mid / heavy duty steel work, Scaffolding etc; batteries can be charged up from 12 volt supply with inverter. £20

Impact wrenches are widely used in many industries, such as automotive repair, heavy equipment maintenance, product assembly (often called "pulse tools" and designed for precise torque output), major construction projects, and any other instance where a high torque output is needed.

In operation, a rotating mass (the hammer) is accelerated by the motor, storing energy, then suddenly connected to the output shaft (the anvil), creating a high-torque impact. The hammer mechanism is designed such that after delivering the impact, the hammer is again allowed to spin freely, and does not stay locked. With this design, the only reaction force applied to the body of the tool is the motor accelerating the hammer, and thus the operator feels very little torque, even though a very high peak torque is delivered to the socket. This is similar to a conventional hammer, where the user applies a small, constant force to swing the hammer, which generates a very large impulse when the hammer strikes an object. Because the hammer spins and has velocity before impacting the anvil, the hammer has momentum. Because it has momentum, it must have kinetic energy. Energy is not stored over time, but rather, energy is stored with velocity. This energy is absorbed by the bolt, nut, or screw in question, and since the collision is (theoretically) an elastic collision, most of the kinetic energy of the hammer is transferred to the bolt that is to be turned. This is contrasted with a regular drill that only applies a torque to the bolt. There is no hammer that reaches a set velocity before hitting an anvil; there is no extra energy to apply to a bolt. The hammer design requires a certain minimum torque before the hammer is allowed to spin separately from the anvil, causing the tool to stop hammering and instead smoothly drive the fastener if only low torque is needed, rapidly installing/removing the fastener.