SAFETY  PRECAUTIONS Hammers  are  dangerous  tools  when  used carelessly  and  without  consideration.  Practice  will help you learn to use a hammer properly. Some  important  things  to  remember  when  using a  hammer  or  mallet  follow: · Do  not  use  a  hammer  handle  for  bumping parts in assembly, and never use it as a pry bar. Such abuses will cause the handle to split, and a split handle  can  produce  bad  cuts  or  pinches.  When  a handle splits or cracks, do not try to repair it by binding  with  string,  wire,  or  tape.  Replace  it. · Make  sure  the  handle  fits  tightly  on  the  head. · Do not strike a hardened steel surface with a steel hammer. Small pieces of steel may break off and injure someone in the eye or damage the work. However,  it  is  permissible  to  strike  a  punch  or  chisel directly  with  a  ball-peen  hammer,  because  the  steel  in the heads of punches and chisels is slightly softer than that  of  the  hammerhead. WRENCHES A wrench is a basic tool that is used to exert a twisting force on bolt heads, nuts, studs, and pipes. The  special  wrenches  designed  to  do  certain  jobs  are, in most cases, variations of the basic wrenches that are described in this section. The best wrenches are made of chrome vanadium steel. Wrenches made of this material are lightweight Figure  1-3.-Open-end  wrenches. and  almost  unbreakable. This is an expensive material,  however,  so  the  most  common  wrenches found in the Navy are made of forged carbon steel or molybdenum  steel.  These  latter  materials  make  good wrenches, but they are generally built a little heavier and bulkier to achieve the same degree of strength as chrome  vanadium  steel. The size of any wrench used on bolt heads or nuts is  determined  by  the  size  of  the  opening  between  the jaws of the wrench. The  opening  of  a  wrench  is manufactured  slightly  larger  than  the  bolt  head  or  nut that it is designed to fit. Hex-nuts (six-sided) and other  types  of  nut  or  bolt  heads  are  measured  across opposite  flats  (fig.  1-3).  A  wrench  that  is  designed  to fit a 3/8-inch nut or bolt usually has a clearance of from 5 to 8 thousandths of an inch. This clearance allows  the  wrench  to  slide  on  and  off  the  nut  or  bolt with a minimum of “play.” If the wrench is too large, the points of the nut or bolt head will be rounded and destroyed. There  are  many  types  of  wrenches.  Each  type  is designed  for  a  specific  use.  Let’s  discuss  some  of them. OPEN-END  WRENCHES Solid, nonadjustable wrenches with openings in one  or  both  ends  are  called  open-end  wrenches.  (See fig. 1-3.) Usually they come in sets of from 6 to 10 wrenches, with sizes ranging from 5/16 to 1 inch. Wrenches with small openings are usually shorter than wrenches with large openings. This proportions the lever advantage of the wrench to the bolt or stud and helps prevent wrench breakage or damage to the bolt or  stud.  One  exception  exists. Hydraulic  piping  installations  for  catapult  and arresting gear are often in close spaces. During certain phases of hydraulic maintenance it may be impossible  to  swing  an  ordinary  wrench  because  of  its length.  Ordinary  wrenches  that  are  normally  available increase in length as their size increases. Thus, when a large-size wrench is needed, the length of the wrench  sometimes  prevents  its  use,  due  to  the  space available  to  swing  the  wrench.  The  Bonney  wrench, shown in figure 1-4, is an open-end wrench that may be used to great advantage because of its thickness and  short  length.  This  wrench  is  normally  procured in the larger sizes, although it is available in a range of  sizes  to  fit  most  hydraulic  fittings. 1-4