Brother HL Series User Manual page 52

Driver and Software
Automatic Duplex Printing (HL-2240D / HL-2242D / HL-2250DN / HL-2270DW only)
 For Mac OS X 10.4.11
a
Select Layout.
b
Choose Long-edged binding or Short-edged binding in Two-Sided.
c
Select Paper Handling.
d
Choose All pages in Print and click Print. You can print pages on both sides of the paper.
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