Selecting the Best Air Impact Wrench

Explore MSC Industrial Supply’s technical guide to learn everything about air impact wrenches, from selecting the right torque to understanding joint types.

Air Impact Wrenches

An air impact wrench, also known as a pneumatic impact wrench, is a type of power tool used to tighten or loosen fasteners using compressed air. It features a high-RPM rotary-vane air motor connected to a hammering mechanism. This design converts the motor’s energy into a series of high-intensity rotary blows, allowing for the assembly and removal of various fasteners.

Pneumatic impact wrenches excel at delivering fast, free-speed rundown before engaging their impactful hammering action to remove stubborn fasteners. Some models of air impact wrenches weigh as little as 2.5 lbs., but despite their lightweight design, they can provide impressive torque levels, often exceeding 280 ft/lbs.

Bolt or Fastener Size

The size and type of bolts or fasteners, along with the required torque, influence the choice of the pneumatic impact wrench for your application. Consulting an Impact Wrench Bolt Selection Chart can help determine the appropriate drive size and torque output of your air impact wrench.

Torque Requirement

Torque needs are dictated by the fastener size, joint type, and accessories being used. When using tools like an extension bar and/or a universal joint, select an impact wrench with a higher torque output to compensate for the 15–20% torque loss these accessories typically cause.

Joint Type

Joints are divided into either hard joints or soft joints, and understanding joint types is crucial. Hard joints, also referred to as hard slam joints, are metal-to-metal connections with less than 30° of fastener rotation required to achieve full torque. Soft joints are connections that compress materials such as gaskets, requiring at least 720° of fastener rotation after seating.

Handle Configuration

At MSC Industrial Supply, you can find a variety of handle styles of air impact wrenches. The most popular one is the pistol grip, which is common on larger impact wrenches (1" and 1½" drives). The straight inline handle design is usually found on smaller air impact wrenches, typically 3/8" and 1/4" hex drives.

Socket Retainer Types

Socket retainers secure sockets or accessories to the wrench. Common types include:

Ring: Ideal for automotive applications where sockets are changed frequently.
Pin: Used in industrial assembly for repetitive tasks with a fixed fastener size.
Combination Ring/Thru-hole: Popular in heavy-duty automotive and industrial settings for 3/4" drive sizes and above.
Quick Change: Found on small air impact drivers with ¼" hex quick-change retainers.
Spline Drive: Commonly found on large wrenches for off-road vehicle service, steel erection, and high-torque requirements.

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