Use the following tools when placing fabrication parts.
When you select a part on the MEP Fabrication Part palette, the Modify | Place Fabrication Part tab provides the following options for placing a fabrication part:
Edit Part: opens the Edit Part dialog where you can edit parameters for dimensions and connectors. 
Rotate Part: rotates the part around its connector. You can also press the spacebar. When placing a fitting such as a tee or a tap, hold Shift and press the spacebar to rotate the orientation of the fitting. Note: Rectangular fittings rotate in 90 degree increments; round fittings rotate in 45 degree increments.
Toggle Connector: toggles the connector. You also press the up arrow. Note: Toggling the connector modifies which open connector is attached to the cursor during placement.
Insert Part: places a tee, valve, damper, or in-line equipment on a straight duct segment in an existing run. Note: This functionality is available only to students and to Autodesk Maintenance and Desktop Subscription customers for Revit 2016 software releases.
Connect as Tap: places a duct fitting as a tap on a rectangular duct or the flat part of an oval duct. Note: This functionality is available only to students and to Autodesk Maintenance and Desktop Subscription customers for Revit 2016 software releases.
Smart Snapping: enables smart snapping to increase the snap target on connectors. Enable smart snapping when you want to make it easier to connect elements. Disable smart snapping when you want to place elements using standard snapping behavior. 
Show Help Tooltip: displays tooltips in the drawing area while placing a part. You also enter the command HT.