TM 1-1500-204-23-9 available  as  ratchet-types,  which  allow  the  screw  to  be driven without having to remove the tip from the screw head. (4) Ratchet   screwdrivers.     The   ratchet,   or   spiral, screwdriver shown in figure 4-16 is fast acting in that it turns the screw when the handle is pulled back and then pushed  forward.    It  can  be  set  to  turn  the  screw  either clockwise  or  counterclockwise,  or  it  can  be  locked  in position   and   used   as   a   standard   screwdriver.      The ratchet  screwdriver  is  not  a  heavy-duty  tool  and  should be used only for light work. Figure 4-16.  Ratchet Screwdrivers NOTE When using a spiral or ratchet screwdriver,  extreme  care  must  be  used to maintain constant pressure and prevent  the  blade  from  slipping  out  from the slot in the screw head.  If this occurs, the   surrounding   structure   is   subject   to damage. (5) Nonmagnetic   screwdriver.       The   nonmagnetic screwdriver  is  shaped  like  a  common  screwdriver,  but the  blade  is  made  of  brass  so  as  to  have  no  magnetic effect.  It is used for compensating compasses. b. Safety.  The following precautions must be kept in mind when using screwdrivers: Ensure that the handle of the screwdriver is clean. • Do    not    use    a    screwdriver    for    prying, punching, chiseling, scoring, or scraping. • Do   not   use   a   screwdriver   to   check   an electric  circuit  since  an  electric  arc  will burn the tip and make it useless.  In some cases, an electric arc may fuse the blade to the unit being checked. • When   using   a   screwdriver   on   a   small part,  always  hold  the  part  in  the  vise  or rest  it  on  a  workbench.    Do  not  hold  the part in the hand, because the screwdriver may    slip    and    cause    serious    personal injury. c. Use   The following paragraphs describe the use of various types of screwdrivers. (1) Proper fit.  Select a screwdriver large enough so the  blade  fits  closely  in  the  screw  slot.    A  loose  fitting blade  can  slip  and  cause  burring  of  the  screw  slot  and damage   to   the   blade.      Proper   and   improper   fits   are shown in figure 4-17.  It is important that the screwdriver be   held   firmly   against   the   screw   to   prevent   it   from slipping  and  possibly  injuring  the  mechanic  or  scarring the work. (2) Use  of  screwdriver.    A  screwdriver  is  used  as follows: (a) Insert  the  screwdriver  tip  into  the  screw slot of the screw. (b) Turn   the   screw   as   required.      Keep   the screwdriver in line with the screw. (3) Use  of  offset  screwdriver.    The  procedure  for using  an  offset  screwdriver  is  as  follows  (see  figure  4- 18): Figure 4-17.  Proper Fit of Screwdrivers 4-6