Kyocera FS-1020D Operation Manual page 40

Setting the Duplex Path of the Custom Paper Type
You can set whether or not duplex printing will be allowed for each custom
paper type.
The default setting is Enable.
1
Click the MENU button on the start-up screen.
2
The Menu dialog box appears. Select and double click Media Type
and the paper types are displayed.
3
Select and double click Custom 1, then click Duplexer. You can
toggle the setting related to duplex printing between Enable and
Disable using the radio buttons on the right side of the screen.
1-30
Media Type
Duplex Printing
Duplexer
Paper