Getting the Most From Impact Sockets

By Richard B. Wright, President, Wright Tool Company

Because impact sockets take such abuse, it is important to choose the right socket and use it correctly. Knowing the proper torque, choosing the proper drive size and following other safeguards will ensure the life of both sockets and fasteners.

While maintenance mechanics expect a great deal from socket wrenches turned by hand, they expect even more from sockets driven by air-operated impact guns. To make impact sockets usable anywhere manual sockets can be used, mechanics want impact sockets to be the same diameter as hand-driven sockets. But mechanics do not want to compromise safety and tool life to get the desired socket nose diameter.

Impact hammers pound away at sockets harder and faster than even the strongest mechanic can manually. So, until recently, realizing the mechanics' demands seemed impossible. Now, however, you can get impact sockets close enough in size to hand sockets that they work nearly anywhere a hand socket will. At the same time, these sockets provide for safety and reasonable tool life.

The "secret" of these new sockets is more surface contact area between the socket and the fastener (nut or bolt head), thereby reducing damage to the fastener and providing more efficiency in driving it.

Factors in safe, efficient fastening
A better socket is only one feature of safe and efficient fastening. Following are some tips for users of all impact sockets. The goal is to be sure you tighten fasteners to their full specified torque and get as much tool life as is consistent with that torque.

"But," you ask, "why wouldn't it be more economical to pull high strength bolts to less than full load?"

The answer is that by doing so, you sacrifice quality, along with safety. Also, because of the high cost of fastening-including the hole, the fastener and assembly-engineering economics dictates usingas few fasteners as possible to do the job. This means, on a correctly engineered job, you must tighten each fastener to the specified torque without overtightening, which may cause a loss in strength.

But what does all of this mean? It means you have to know the proper torque and drive size to get a job done safely and properly from beginning to end.

Knowing the right torque
Fasteners requiring the same socket size (wrench opening) differ in strength. Therefore, to tighten a fastener safely, you always should ask a design or product engineer to specify the required torque for every assembly fastener.

After determining the proper torque, choose a size and model of impact gun that will deliver at least that much torque. Do not use an oversized impact gun, because you may have difficulty controlling the tightening torque. You may end up over-torquing, which could weaken or break the fastener.

Next, check the specified torque against the value listed in Table 1 for the drive size and wrench opening. Don't exceed the values listed. Doing so may result in wrench breakage and an inability to tighten the fastener. You will obtain substantially better socket life by applying 70 percent or less of the values in Table 1. This practice also will ensure easy disassembly for repair. After all, the force required to remove a fastener that has been in service for some time always is more than the force required to tighten the fastener.


Choosing the proper drive size
No drive size always is correct for a particular size of socket. The correct size depends on the required torque of the fastener and the capabilities of the gun, as well as the strength of the male driving square.

Most sockets are made in several drive sizes. For example, you can find 5/16-in. opening sockets in 3/8- in., 1/2-in. and 3/4-in. drive sizes. Each has a different purpose and different application. The outside diameters vary and, as Table 1 shows, the strengths vary as well. Strength increases with drive size and with the wrench opening, up to the limit imposed by the strength of the driving square.

Understanding impact socket life
Whether you are tightening or removing a fastener, the most important factor in determining socket life is the peak torque. For safety, do not exceed the values listed.

As the maximum load increases as a percentage of the value of Table 1, tool life decreases. Thus, if you continue to exceed the listed value for peak torque, the socket eventually will crack. If the load is light, it will crack as a result of being worn to the point where the fastener cams the socket. Cracked or worn out sockets should never be used.

Another important factor is the quality of the socket. Sockets differ in material, design and manufacturing. These varying factors also cause sockets to differ in performance.

For example, as mentioned earlier, now there are impact sockets with newly designed openings. On these units, the sides of the socket opening are angled so that they meet hexagonal fasteners more squarely and without distorting corner loading. The new design is particularly important in non-manual, impact applications, because the hammer blow of the gun is distributed over a wider area of both the fastener and the socket.

As more designs such as these are introduced, the life of impact sockets will increase substantially, as will safety in their use.

About the Author:
Richard B. Wright is president of Wright Tool Company, a leading manufacturer of professional-quality sockets and wrenches. Located in Barberton, Wright Tool manufactures more than 3,300 tools for the industrial, contractor, and MRO markets.

Mr. Wright holds a degree in Mechanical Engineering from the California Institute of Technology and an M.B.A. degree from the University of Pennsylvania Wharton School. A licensed engineer, Mr. Wright holds several patents in the field of hand tools and electrical instrumentation.