Apple Final Cut Pro 7 - Manual (Page 494)

To clear both In and Out points at the same time
Do one of the following:
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Press Option-X.
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Control-click in the scrubber bar, then choose Clear In and Out from the shortcut menu.
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Option-click the Mark Clip button.
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.
494 Chapter 33 Setting Edit Points for Clips and Sequences