How To Choose The Proper Socket Wrench

By Richard B. Wright, President, Wright Tool Company

Professional socket wrenches are about the most versatile and frequently used tools in plant maintenance. The versatility of these tools is shown by the variety of sizes, designs, drives and "specials" that are in every maintenance tool box.

However, it is the variety and versatility of these tools that can lead to their incorrect use. Misapplications can seriously damage the wrench, the fastener, the equipment, or even the user. Most mechanics know that use of the wrong wrench or incorrect use of the right wrench can result in injury. User safety must always come first: Expediency is no justification for an accident.

One of the most common misapplications involves an incorrect fit--too much clearance between the wrench and the fastener. This can damage either the wrench or the fastener or both. Points can be stripped off the wrench or the wrench can be broken as a result of excess camming forces. A badly worn wrench can be 30% weaker than a new wrench.

Whether the cause is an excessively worn wrench, an undersized fastener, a fastener with rounded corners or use of mis-sized wrenches and fasteners, poor fit will result in insufficient bearing surface between wrench and fastener to transmit the load that is required to remove the fastener. To make matters worse, if the mechanic tries to turn the fastener when there is insufficient contact area, the corners of the fastener will be further rounded, or the fastener will be otherwise deformed so there is even less contact area.

If the wrench has been broken, a new wrench can be used, and may very well work. But if the fastener is damaged, a new wrench will not work because of inadequate contact between the wrench and the fastener. The time to decide when a wrench is worn out is before it is used, rather than after it chews up a fastener.

It is also important to ensure that the wrench is placed all the way onto the fastener. Extra care should be taken when the mechanic cannot actually see the wrench fitting the fastener. Also, moving an impact gun from removing one fastener to another without stopping results in the gun applying full load to a partially engaged wrench. This is not as much of a problem in assembly, but it is still not good practice because it can damage the fasteners enough to create problems on removal.

HAND OR IMPACT SOCKETS?

The conditions of the job will determine whether it is more practical and convenient to turn the wrench by hand or with an impact gun, or, for very large wrenches, a hydraulic driver. The important thing to remember is that hand sockets should never be turned by either impact guns or hydraulic wrenches. Hand sockets are designed and manufactured only for hand use and differ substantially from impact sockets which are designed for greater strength under the conditions of shock loading produced by impact guns. For the heavy loads frequently encountered with 3/4-in. and larger drives, impact guns are safer than hand. The temptation to use a cheater bar or hammer on the handle of the socket wrench should be avoided.

Fastener removal must always be treated as a heavy-duty job. The torque required to remove a fastener is often more than twice the torque that was used at installation. Lubrication that is almost always on fasteners at the time of installation works its way out, corrosion occurs, and the threads may become deformed during installation by slight thread form errors or "stretching" of the bolt. Rust and corrosion significantly increases removal torque.

WHICH DRIVE?

Although smaller socket drives are lighter and handier, they are not as strong as the opening in a larger drive. A typical wrench opening is made in three different size drives. For example, a 3/4-in. opening hand socket is available in 3/8-, 1/2-, and 3/4-in. drive. The wall thickness and, therefore the strength, is larger in the 1/2-in. drive and even larger in the 3/4-in. drive. A 3/8-in. drive square cannot have enough strength to apply all the torque that may be required for this size opening.

For this reason, this size wrench should be used only when there is not sufficient room for a 1/2-in. drive, or if the material is of low strength, such as brass or copper.

For higher strength fasteners, the 3/4-in. drive is recommended because these stronger fasteners require much more torque and are typically used in more critical applications. If the wrench is to be turned by an impact gun, a 3/8-in. drive is not recommended because of the higher torque and shock loading that impact guns produce.

The general rule for standard industrial fasteners is: Use the largest drive possible. Not only is strength increased, but also leverage, because of longer handles.

Another advantage of larger drives is longer handles and, therefore, less required force. In many cases, this is more convenient, but, in installing fasteners, torque should not be judged by convenience but rather with a torque wrench following the manufacturer's specifications. On high-strength bolting applications, only a calibrated, accurate torque wrench should be used.

For critical bolting applications, a torque angle tool is recommended. If torque specifications are not available, proper tightening torque for the fastener can be found in the torque wrench manual.

An experienced mechanic will have a sense of which should be used in conjunction with the torque wrench. If the joint doesn't feel right, it probably is not in good condition. Threads are possibly crossed or malformed. An experienced mechanic will detect this problem, but a torque wrench will not. If a joint is cross-threaded and tightened to the proper torque, it will not be nearly as tight as it should be.

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 3,000 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.