| Constant | Description |
| BEND | A fitting with typically two ports used to change the direction of flow between connected elements. |
| CONNECTOR | Connector fitting, typically used to join two ports together within a flow distribution system (e.g., a coupling used to join two pipe segments). |
| ENTRY | Entry fitting, typically unconnected at one port and connected to a flow distribution system at the other (e.g., a breeching inlet). |
| EXIT | Exit fitting, typically unconnected at one port and connected to a flow distribution system at the other (e.g., a hose bibb). |
| JUNCTION | A fitting with typically more than two ports used to redistribute flow among the ports and/or to change the direction of flow between connected elements (e.g, tee, cross, wye, etc.). |
| OBSTRUCTION | A fitting with typically two ports used to obstruct or restrict flow between the connected elements (e.g., screen, perforated plate, etc.). |
| TRANSITION | A fitting with typically two ports having different shapes or sizes. Can also be used to change the direction of flow between connected elements. |
| USERDEFINED | User-defined fitting. |
| NOTDEFINED | Undefined fitting. |