Apple Final Cut Pro 7 - Manual (Page 544)

2 Specify an In point for the source clip in the Viewer.
In point
3 In the Timeline, move the playhead to the middle of the gap you want to fill.
Move the playhead into
the gap.
4 Choose Mark > Mark Clip (or press X) to set In and Out points around the gap.
Note: You must select the Auto Select controls for the tracks containing the gap. For
more information, see
“Using Auto Select to Specify Tracks for Selections.”
In and Out points
544 Chapter 36 Three-Point Editing