Click Centerline 
on the Sketch toolbar, or click Tools,
Sketch Entities, Centerline.
The pointer changes to 
.
Click to start the centerline.
Drag, or move the pointer and click, to set the end of the centerline.
Use centerlines to create symmetrical sketch elements and revolved features, or as construction geometry.
To create a centerline:
Click Centerline on the Sketch toolbar, or click Tools,
Sketch Entities, Centerline.
The pointer changes to .
Click to start the centerline.
Drag, or move the pointer and click, to set the end of the centerline.
To change the centerline properties:
In an open sketch, select a centerline and edit its properties in the Line PropertyManager.