Apple Final Cut Pro 5 - Manual (Page 456)

Chapter 7 Setting Edit Points for Clips and Sequences 121
II
To clear an Out point, do one of the following:
m Press Option-O.
m Option-click the Mark Out button.
m Control-click in the scrubber bar, then choose Clear Out from the shortcut menu.
m In the Viewer or Canvas, drag an Out point vertically off the scrubber bar, either up or down.
To clear both In and Out points at the same time, do one of the following:
m Press Option-X.
m Option-click the Mark Clip button.
m Control-click in the scrubber bar, then choose Clear In and Out from the shortcut menu.
Note: If you set an In point later than an Out point, the Out point is automatically removed.
If you set an Out point earlier than an In point, the In point is automatically removed.