TM 10-3930-659-20 2-24. 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  44,  Appendix  F).    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. 2-25. LOCKWIRE. a. Always use nonelectrical wire (Item 41, Appendix C). b. Drilled head screws and bolts usually do not require lockwiring if they are installed with self-locking nuts or lockwashers. TA706718 2-13