TM 10-3930-659-34 2-21.  TUBES AND COMPRESSION FITTINGS. a.    Tubes with inverted nuts and compression fittings are designed for one time assembly.  Once assembled,  they  must  be  replaced  as  a  unit  if  any  parts  are  found  defective.    Used  parts  may  not seal properly when used with new ones. b.    Used  tube  assemblies  in  good  condition  can  be  installed  to  their  original  location  without leaking. c.    Assemble new tubes, compression sleeves, and inverted nuts as follows: (1) Slide inverted nut onto end of tube. (2) Slide compression sleeve onto end of tube. (3) Repeat    previous    two    steps    for other end of tube as required. d.    Install new tube assemblies as follows: (1) Insert  end  of  tube  as  far  as  it  will  go  into  compression  fitting  to  which  tube  is  being installed. (2) Twist Inverted nut into compression fitting and tighten inverted nut against compression sleeve with open-end wrench (Item 71, Appendix E).  Compression sleeve will  clamp  down  around tube and conform to internal surface of compression fitting and inverted nut. (3) Repeat previous two steps for other end of tube as required. 2-22.  LOCKWIRE. a.    Always use nonelectrical wire (Item 59, Appendix B). b.    Drilled head screws and do Its usually do not require lockwiring if they are installed with self- locking nuts or lockwashers. 2-12