WARNING TM  5-6675-302-14&P 4-8. Light Concealing Hood (Model 242406 Only). a.  General.  The  light  concealing  hood  (fig.  4-3) consists of a bracket, barrel, spring clip and cotter pin  hinge,  This  assembly  slides  over  the  target  to confine  all  light  at  one  point  during  night  opera- tions. b.  Removal. (1) Release spring clip from target. (2) Remove bracket by sliding bracket over the top of target. (3) Remove  barrel  from  bracket  with  a  twist- like  turn. C. Cleaning and Inspecting. (1)  Brush  all  dirt,  dust,  and  foreign  matter from the bracket and hood. (2) Inspect for breaks or other damage; repaint worn spots. d. Installation. Reassemble lustrated in figure 4-3. 4-9. Light Concealing Hood Only). and  install  as  il- (Model  USATS-79 a. General. The light concealing hood (fig. 4-4) is a  single  piece  of  molded  rubber  which  slides  over the  target  plate  to  limit  stray  light  during  night operations. b.  Removal.  Slide  the  light  concealing  hood  up and off the target plate (fig. 4-4). c. Cleaning and Inspection. (1)  Brush  all  dirt,  dust,  and  foreign  matter from the light concealing hood. (2)  Inspect   for   breaks,   cracks,   or’   other damage. d.   Installation.   Install   light   concealing   hood (figure 4-4). 4-10. Tribrach Assembly. a.  General.  The  tribrach  assembly  consists  of the  tribrach,  leveling  screw,  optical  plummet,  cir- cular   level,   and   base   plate   assemblies.   The tribrach   assembly   facilitates   quick   and   accurate installation  and  removal  of  a  target  assembly  to  a preleveled  base  attached  to  a  tripod  head;  thus, enabling  the  operator  to  shift  the  instrument  bet- ween  established  stations,  without  having  to  level or realine the target assembly each time it is mov- ed. b.   Removal.   Refer   to   figure   4-3   for   model 242406,  or  figure  4-4  for  model  USATS-79,  and remove the tribrach assembly as follows: 4-6 (1) Loosen  the  tribrach  lock  screw.  Rotate  the tribrach  lock  lever  counterclockwise,  and  remove the target assembly from the tribrach assembly. (If target assembly is not mounted, see (2) below). (2) Unscrew  the  bridge  screw  (43,  fig.  4-5  for model 242406, or 11, fig. 4-6 for model USATS-79), and remove the tribrach assembly from the tripod. C. Cleaning and Inspection. Brush all dirt, dust, and  foreign  matter  from  the  tribrach  components. Wipe  all  surfaces  clean  with  a  soft,  lint-free  cloth moistened   with   an   approved   cleaning   solvent. Thoroughly clean all bearing surfaces on which the tapered  locking  wedges  ride.  Inspect  the  three leveling  screws  for  improper  operation.  They should  turn  smoothly  and  evenly,  yet  require  a moderate  amount  of  force  exerted  by  thumb  and forefinger,  to  turn  without  backlash.  Lubricate bearing  surfaces  sparingly  before  reassembling the  tribrach  assembly  to  the  theodolite.  Replace  a defective  tribrach  assembly. d. Installation.  Reverse the procedures describ- ed in b, above. 4-11. Tripod Assembly. a.  General.  The  tripod  is  equipped  with  exten- sion legs and consists of the tripod head, tripod leg assemblies,  and  the  cover  plate.  A  plumb  bob  and tripod   wrench’   on   model   242406   or   key,   socket screwhead  on  model  USATS-79  are  kept  in  the tripod  accessory  case,  which  is  mounted  on  one  of the  tripod  legs.  The  plumb  bob  is  used  along  with the tripod to center the instrument exactly over the station  point,  On  model  242406  the  tripod  wrench is  used  to  tighten  or  loosen  the  clamping  screws located   under   the   tripod   head   that   secures   the tripod   leg   assemblies   in   position.   On   model USATS-79 the key, socket screwhead performs the same function as the tripod wrench. b.  Disassembly.  On  model  242406  refer  to  fig- ure  4-5  and  disassemble  the  tripod;  on  model USATS-79 refer to figure 4-6. c.  C1eaning and Inspection. Clean   parts   in   a   well-ventilated   area. Avoid  inhalation  of  solvent  fumes  and prolonged  exposure  of  skin  to  cleaning solvent.  Wash  exposed  skin  thoroughly. Dry   cleaning   solvent   (Fed.   Spec. P-D-680) used to clean parts is potential- ly  dangerous  to  personnel  and  property. Do not use near open flame or excessive heat.  Flash  point  of  solvent  is  100F  to 138F (38C to 59C).