Dell C2660dn User Manual page 211

2 Extend the extension tray as necessary.
3 Slide the width guides to the edge of the tray. Th width guides should be fully extended.
4 Insert all media facing up and top edge first into the MPF.
NOTE:
Do not force the print media into the MPF.
5 Slide both width guides until they rest lightly against the edge of the print media stack.
NOTE:
Do not force the print media into the MPF
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