Kyocera DU-31 Instructions page 9

3.
Remove the duplexer from the packing materials and install in the printer
as shown in the figure. Install so that the left and right rails are correctly
resting on the rails of the printer.
Rail
4.
Push the DU-31 all the way into the printer.
5.
Close the printer's front cover. This completes installation of the duplexer.
8
Rail