A refresher course on wrench use and safety

The Hand Tools Institute

Wrenches are designed for holding and turning nuts, bolts, cap screws, plugs and various threaded parts. Quality wrenches, regardless of their type, are designed to keep leverage and intended load in safe balance. Standard wrench types are available with both American Standard inch and metric openings. Special wrenches are also available for servicing and overhaul of certain widely used equipment.

Different types of wrenches are of different strengths and are designed for different purposes, such as for wrenching high-strength fasteners. Box end and socket type wrenches, because they surround the fastener head, are the strongest types of wrenches and have less chance of slipping off the fastener. Open end, flare nut and adjustable wrenches are not as strong as the corresponding sizes of box or socket wrenches because they do not surround the fastener head, and are not intended for heavy loads, such as breaking loose frozen fasteners.

Proper use and care of wrenches

1) Select a wrench whose opening exactly fits the nut. If the wrench is not exactly the correct size for the fastener, it may damage the corners of the fastener, slip or break. Care should be exercised in selecting only inch wrenches for inch fasteners and only metric sizes for metric fasteners

2) Always pull on a wrench handle and adjust your stance to prevent a fall if sudden release occurs.


3) To free a "frozen" nut or bolt, use a striking-face box wrench or a heavy-duty box or socket wrench. Application of penetrating oil to the fastener threads beforehand is recommended.


Avoiding abuse/misuse
1) Never use a pipe extension or other form of "cheater" to increase the leverage of any wrench.


2) Never cock an open-end wrench. Be sure the nut or bolt head is fully engaged.


3) Avoid over- or under-torquing. A torque wrench will permit tightening to the exact torque required.

4) Never expose any wrench to excessive heat that may change the hardness and metal structure and ruin the tool.

5) Never grind a wrench, even as a means of identification.

6) Never use a wrench that has been damaged by being bent, cracked, or severely worn.

7) Electrical warning: Always disconnect the power before working on electrical equipment or devices. Never depend on an insulated tool to protect you from electricity. Ordinary plastic-coated handles are designed for comfort and provide no electrical insulation. Other tools, such as insulated and insulating, that have high-dielectric insulation are so identified. The high-dielectric insulation is intended only as secondary protection and for use by trained personnel.


Sockets, handles and attachments
There are two common types of sockets – hand and impact. Each is different in design and hardness. Hand sockets usually have a bright finish but may have a black finish. Impact sockets have a black finish and usually have thicker walls.

Sockets are made in regular length and deep length. Openings may be 12-, 8- or 6-point or square. Spark plug sockets have rubber inserts or other devices to hold the plug. Universal joint sockets are also available.

Proper use and care
1) S elect size and type of socket to fit nut (inch/metric).

2) Select the largest possible drive size – many sockets are available with smaller drive sizes than should be used at high load. They may be used for run-up (pre-tightening) or other low-load applications.

3) Select appropriate handle.

4) Select extension and joint.

5) Caution: The possibility exists for a lower torque-rated accessory or socket or a combination of accessories and socket to be used in conjunction with a higher-rated ratchet or drive tool.

6) Care should be exercised so as not to overload the lowest-rated component.

7) Caution: Adapters and attachments reduce the load capacity of the tool, and should not be used under heavy load.

8) Periodic cleaning and inspection of handles, sockets and attachments is very important. Many manufacturers supply parts, repair kits and instructions for servicing their ratchet wrenches and handles. Repairs to the handles or ratcheting mechanism should be made with the manufacturer's own parts.


Avoiding Abuse/Misuse
1) Never increase the leverage of a wrench handle by use of a pipe or other form of cheater on the wrench handle.

2) Never use hand sockets on power drive or impact wrenches.

3) When using adapters, remember that when adapting "down" (big handle, small socket), you build up tremendous torque potential and risk breaking the socket.

4) When adapting "up" (small handle, big socket), there is a risk of applying too much force to the handle and it may break.


When to repair or replace

  • Do not attempt to repair sockets.
  • Discard sockets or attachments with any sign of cracking.
  • Discard any socket with rounded or damaged wrench openings, or with worn or deformed drive ends.


About the author
This article has been provided by the Hand Tools Institute, a trade organization comprised of manufacturers of hand tools and tool storage products. This article is an excerpt from the upcoming fourth edition of the HTI publication “Guide to Hand Tools: Selection, Safety Tips, Proper Use & Care”. To learn more, visit www.hti.org.

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