To Insert a Part or Feature From a Custom Content Library (AutoCAD Mechanical Toolset)

Click Content tabLibrary panelContent Libraries. Find
In the Content Libraries dialog box, in the Content panel, expand the Custom Content node and locate the part/feature to insert.
In the Content Libraries dialog box, in the Details panel, click the view to insert.
Specify the insertion point and rotation when prompted to.
If the Size Selection dialog box displays, specify the size of the part/feature in the Predefined Parameters section.
Note: The Size Selection dialog box displayed only if the part/feature is setup for multiple sizes.
If AutoCAD Mechanical toolset prompts you to drag to specify the size, drag the custom grips.
Note: This feature is enabled only if the part is setup for resizing via dragging