| 138 / | HD | PIPES AND TUBULAR CONDUITS |
| 111 | | PLURAL DUCT {4} |
| 112 | DF | .~> With spacer and encircling element |
| 113 | DF | .~> Surrounding radially spaced duct with axially spaced supports for internal duct |
| 114 | DF | .~> Coaxial |
| 115 | DF | .~> Longitudinally extending common wall {2} |