Figure  1-4.-Bonney  wrenches. Open-end  wrenches  may  have  their  jaws  parallel to the handle or at angles anywhere up to 90 degrees. The average angle is 15 degrees (fig. 1-3). This angular  displacement  variation  permits  selection  of  a wrench suited for places where there is room to make only a part of a complete turn of a nut or bolt. If the wrench  is  turned  over  after  the  first  swing,  it  will  fit on the same flats and turn the nut farther. After two swings on the wrench, the nut is turned far enough so that a new set of flats are in position for the wrench, as  shown  in  figure  1-5. Handles are usually straight, but may be curved. Those  with  curved  handles  are  called  S-wrenches. Other open-end wrenches may have offset handles. This  allows  the  head  to  reach  nut  or  bolt  heads  that are sunk below the surface. BOX WRENCHES Box wrenches (fig. 1-6) are safer than open-end wrenches since there is less likelihood they will slip off the work. They completely surround, or box, a nut  or  bolt  head. The  most  frequently  used  box  wrench  has  12 points or notches arranged in a circle in the head and can be used with a minimum swing angle of 30 degrees. Six- and eight-point wrenches are used for heavy  duty;  twelve-point  for  medium,  and  sixteen  for light-duty  only. One advantage of the 12-point construction is the thin wall. It is more suitable for turning nuts that are hard to get at with an open-end wrench. Another advantage  is  that  the  wrench  will  operate  between obstructions  where  the  space  for  handle  swing  is limited. A very short swing of the handle will turn the nut far enough to allow the wrench to be lifted and  the  next  set  of  points  fitted  to  the  comers  of  the nut. One disadvantage of the box-end wrench is the time loss that occurs whenever a craftsman has to lift the wrench off and place it back on the nut in another position when there is insufficient clearance to spin the  wrench  in  a  full  circle. COMBINATION  WRENCH After a tight nut is broken loose, it can be unscrewed  much  more  quickly  with  an  open-end wrench than with a box-wrench. A  combination box-open end wrench (fig. 1-7) comes in handy in a situation of the type. You can use the box-end for breaking  nuts  loose  or  for  snugging  them  down,  and the open-end for faster turning. The  box-end  portion  of  the  wrench  can  be designed with an offset in the handle. Notice in figure  1-7  how  the  15-degree  offset  allows  clearance over  nearby  parts. The  correct  use  of  open-end  and  box-end wrenches can be summed up in a few simple rules, most important of which is to be sure that the wrench properly fits the nut or bolt head. When you have to pull hard on the wrench, as in loosening a tight nut, make sure the wrench is seated squarely on the flats of the nut. Pull on the wrench– DO NOT PUSH. Pushing a wrench is a good way to skin your knuckles if the wrench  slips  or  the  nut  breaks  loose  unexpectedly.  If it is impossible to pull the wrench and you must push, do it with the palm of your hand and hold your palm open. Only actual practice will tell you if you are using the  right  amount  of  force  on  the  wrench.  The  best way to tighten a nut is to turn it until the wrench has a firm, solid “feel.”   This will turn the nut to proper tightness without stripping the threads or twisting off the bolt. This “feel” is developed by experience alone.  Practice  until  you  have  mastered  the  “feel.” SOCKET WRENCH The  socket  wrench  is wrenches in the toolbox. 1-5 one of the most versatile Basically, it consists of a