T.O.  1-1A-9 TABLE 8-2.  ROCKWELL SCALES, LOADS AND PREFIX LETTERS SCALE PREFIX INDENTOR/PENETRATOR MAJOR LOAD DIAL NUMBERS LETTERS KILOGRAMS A Diamond 60 Black B* 1/16 in Steel Ball 100 Red C* Diamond 150 Black D Diamond 100 Black E 1/8 in Ball 100 Red F 1/16 in Ball 60 Red G 1/16 in Ball 150 Red H 1/8 in Ball 60 Red K 1/8 in Ball 150 Red L 1/4 in Ball 60 Red M 1/4 in Ball 100 Red P 1/4 in Ball 150 Red R 1/2 in Ball 60 Red S 1/2 in Ball 100 Red V 1/2 in Ball 150 Red * Most Commonly Used Scales. The  hardness  method  is  insensitive  in  this  case,  and  recourse  must  be  taken  to  chemical  analysis.    In  this  technical order,  only  the  hardness  method  is  covered.    When  precise  measurements  are  required,  publications  giving  detailed measurements must be consulted. 8-24.  HARDNESS METHOD. 8-25.  Taper or Step Grind The specimen cont2intng the surface on which decarburization is to be measured is prepared so that it can be manipulated on a Rockwell superficial or Vickers hardness tester.  If the specimen is not in the hardened condition,  it  is  recommended  that  it  be  hardened  by  quenching  from  heating  equipment  under  conditions  which  avoid further  change  in  carbon  distribution.    For  the  taper  grind  procedure,  a  shallow  taper  is  ground  through  the  case,  and hardness measurements are made along the surface.  The angle is chosen so that readings spaced equal distances apart will  represent  the  hardness  at  the  desired  increments  below  the  surface  of  the  case.    The  step  grind  procedure  is essentially  the  same  as  the  taper  grind,  except  that  hardness  readings  are  made  on  steps  which  are  known  distances below the surface.  These steps should be ground at pre-determined depths below the surfaces, and of sufficient areas to allow several hardness readings on each flat. 8-26.  The file method is often suitable for detecting decarburization of hardened materials during shop processing, but not for accurate measurement.  Base metals expected to harden above RC60 and foundto    be    file    soft    are    probably decarburized.    Decarburitation  of  base  metal  that  will  not  harden  to  RC60  can  not  be  detected  by  this  method  unless specially  prepared  files  are  used.    The  extent  and  severity  of  any  decarburization  detected  by  this  method  should  be verified by either of the other methods. Change 6  8-9