top of page
  • Writer's pictureFlorian Buder

The art of using a reaction arm correctly

Updated: Jun 20, 2022

The proper application of reaction arms is crucial for a safe operation and longer life span of torque multipliers.

To avoid unnecessary danger, ensure to use the right tool suitable for the actual application. One must not ignore the importance of the reaction arm, which plays a vital role in the safety and wear and tear of tools. The standard reaction arm is supplied with each alkitronic device but does it fit your torque application or sockets? Learn more on the proper use of reaction arms in the following paragraphs.

What is a torque multiplier reaction arm (alkitronic's abbreviation "DMA")?

Most people understand that a socket is attached to the torque multiplier to run a nut down until it feels the torque and stops according to the settings. Without a reaction arm, this wouldn't be possible. The reaction arm is connected to the torque multiplier above the square drive on a product-specific spline to absorb and transfer reaction forces as shown in the following illustration.

The multiplier and the reaction arm begin to rotate in the opposite direction until the arm stops against the reaction surface. The multiplier never transmits torque forces to the operator’s hand, unlike impact wrenches.

Watch the video below to learn more:

What do you have to consider when selecting a reaction arm!

  • The socket is supposed to be even with the bottom end of the reaction arm.

  • The foot of the reaction arm should align

  • 90-degree angle when operating correctly.

Always keep your hands away from the reaction arm and barrel when the tool is in operation to avoid injuries. Watch this short clip to learn more about the proper application of the torque tool:

This technical brochure shows the application of the torque multiplier and the manufacturer's recommended maximum deviation of the reaction arm.

Download pdf version:

Download • 63KB

Reaction forces decrease the further the reaction point is away from the center of the square drive. The reaction may be taken by the reaction bar resting against a solid projection, or by a socket fitting over the head of an adjacent fastener. Reaction forces work in the opposite direction to fastener rotation and would be, for example, at 2,000 lbf.ft.

Output 2000 lbs at 1 ft. radius

Output 4000 lbs at 6 in. radius

Output 6000 lbs at 4 in. radius

Always take torque reaction as far away from the tool as possible to reduce excessive side loads. Where it is necessary to use an extension drive between the output square drive of the tool and the socket, you must provide a balanced reaction. A double-sided reaction bar with both sides taking equal load serves this purpose, otherwise, the tool either forces itself sideways off the fastener or the gears are damaged by the leverage exerted to twist under these conditions.

It is also advisable to have a special reaction bar to cope with torque in excess of 2,000 lbf.ft when the reaction point of contact is less than 4 inches from the center of the square drive. Pieces may be welded onto the standard reaction bar to overcome this problem without detriment.

Customized solutions

If a standard reaction arm is not suitable due to a tricky location or some other obstruction, alkitronic helps you design and manufacture the right reaction arms. Have a look at a couple of examples:

Recent Posts

See All
bottom of page