TM 1-1500-204-23-9 (2) NO GO ring gauges.  The NO GO gauges are slightly smaller than GO gauges, and are distinguished  by  an  annular  groove  cut  in  the  knurled outer surface of the ring. b. Tolerances.  Depending on the use, ring gauges are manufactured to different tolerances.  The following classes   of   gauges   and   their   limits   of   accuracy   are standard for all makes: Class X- Precision  lapped  to  close  tolerances for  many  types  of  masters  and  the highest quality working and inspection gauges. Class Y- Good          lapped     finish     to     slightly increased tolerances. Class Z- Commercial      finish    (ground    and polished,   but   not   fully   lapped)   with fairly wide tolerances. Class ZZ-   Ground only to meet the demand for an   inexpensive   gauge,   with   liberal tolerances. Tolerances  for  ring  gauges  in  each  class  are  listed  in table 3-1. c. Use.    Ring  gauges  are  used  more  often  in  the inspection  of  finished  parts  than  parts  in  process.    The reason   for   this   is   that   the   finished   parts   are   usually readily accessible; whereas, parts in a machine that are supported at both ends would have to be removed to be checked.    A  part  such  as  a  pivot  stud  is  checked  by performing the following procedures (see figure 3-58): (1) Line  the  stud  up  with  the  hole  in  the  GO gauge, and gently press it in.  If the stud will not go in, the  shank  is  too  large.    If  it  will  go  in,  the  stud  is  not oversize. (2) With the stud in the hole, check the piece for  taper  and  out-of-roundness  by  gently  shaking  it  and sensing any wobble. (3) After  checking  the  part  in  the  GO  gauge, check  it  in  the  NO  GO  gauge.    If  the  stud  is  within desired limits, it will not go into the gauge. NOTE The GO ring gauge controls the maximum  dimension  of  a  part  and  NO GO   plug   gauges   control   the   minimum dimension   of   a   hole.      Therefore,   GO gauges   control   the   tightness   of   fit   of mating  parts  and  NO  GO  gauges  control the looseness of fit of mating parts. Table 3-1.  Ring Gauge Tolerances To and Above Including x¹ y² z³ ZZ⁴ 0.029 0.825 0.00004 0.00007 0.00010 0.00020 0.825 1.510 0.00006 0.00009 0.00012 0.00024 1.510 2.510 0.00008 0.00012 0.00016 0.00032 2.510 4.510 0.00010 0.00015 0.00020 0.00040 4.510 6.510 0.00013 0.00019 0.00025 0.00050 6.510 9.010 0.00016 0.00024 0.00032 0.00064 9.010 12.010 0.00020 0.00030 0.00040 0.00080 1 Precision lapped ² Lapped ³ Ground or polished (grinding marks may be in evidence) 4 Ground only 3-26