| 52 / | HD | STATIC STRUCTURES (E.G., BUILDINGS) | 
| 720.1 | DF | SHAFT (I.E., ELONGATED RIGID STRUCTURE) {15} | 
| 721.1 | DF | .~ Stone-like component (e.g., concrete, etc.) {2} | 
| 721.2 | DF | .~.~ Upright {3} | 
| 723.1 |  | .~.~.~ Having shell-like outer layer {1} | 
| 723.2 | DF | .~.~.~.~> Partial sleeve (e.g., collar, etc.) |