• Open-end wrenches come in many different sizes and specifications for a myriad of applications.Wrench image by hugy from Fotolia.com
  
  Open-end wrenches are a vital ingredient of any mechanic's toolbox. With the open end on one side and a closed double hexface ring on the other, the open-end wrench allows precise and versatile access to nuts and bolts in the most recessed and inaccessible locations. When using a wrench to loosen any fastener, you should always use the exact size for the job. Wrenches too large will have play and can “round off” a fastener before turning. Forcing a wrench a millimeter too small onto a fastener can also damage the fastener face.
  
  

Width

• All open-end wrenches have a specific width. Whether in English (inches) or metric (millimeters), the wrench width corresponds to the fastener width. The inside width of the wrench will equal the fastener’s outside width. On the other end of the open-end wrench, the closed ring wrench inside diameter will equal the wrench’s width.
  
  Avoid using metric open-end wrenches on English fasteners or the opposite. Even though it may appear to be a close fit, the minor difference in size between the wrench and fastener can result in fastener damage. Usually, open-end wrenches are cast of a harder metal than the fasteners. This means the fastener will get damaged before any damage to the open-end wrench.
  
  

Length

• No matter the width of the open-end wrench, different wrench sets may have different lengths. Longer wrenches allow greater leverage for turning a fastener. Shorter ones can be used to get access to fasteners not easily accessible with a large tool.
  
  When working on older possibly corroded fastener, having the correct length open-end wrench can be the difference between removing the fastener or possibly breaking it off with too much torque. A long wrench may seem like the easiest way to remove the fastener but using the right wrench is the best way to avoid more complication.
  
  Likewise, when installing fasteners of any age use the correct length wrench for the job. Without using an actual torque wrench, the correct lever length with the open-end wrench will secure the fastener without applying too much force. Over tightening a fastener can possibly damage the nut, the bolt or the surface of the components being fastened.
  
  

Thickness

• Open-end wrenches also have various thickness. A thin wrench will allow the wrench to slide into a tight space to get around the fastener. A thicker wrench will provide more wrench face on the fastener to improve the grip and turning force. Also, different fasteners have different thickness. Putting a thick open-end wrench on a thin fastener could round off the fastener’s face. A thin wrench on a thicker fastener may gouge the fastener without freeing it.