Apple LaserWriter 12/640 PS - Manual (Page 215)

6 Adjust the width guide so that it fits snugly against the paper, but not so tightly that it
might cause binding.
To avoid paper jams, always set the length and width guides to the correct
positions for your particular paper.
7 Insert the paper cassette into the 500-sheet feeder.
Loading the 500-sheet cassette with letterhead and three-hole punched paper
Insert letterhead paper into the 500-sheet cassette face down, with the top of
the letterhead at the front of the tray (the handle end).
If you want to print on both sides of the letterhead paper, place the
letterhead paper face up in the paper cassette, with the top of the page
closest to the handle.
Insert three-hole punched paper into the paper cassette so the holes are
toward the left side of the 500-sheet cassette.
Make sure paper fits under this corner bracket.
Orient three-hole punched paper
and letterhead paper as shown.
215 Loading Paper