Kyocera FS-C5015N Advanced Operation Manual page 125

Options
For detailed information on installing the paper feeder, see the manual
supplied with the paper feeder.
DU-301 Duplex Unit
The duplex unit is attached to the bottom of the printer and allows you to
print onto both sides of the paper. Printing on both sides can be performed
using ISO A4, ISO A5, JIS B5, letter, and legal sized paper.
For detailed information on installing the duplex unit, see the manual
supplied with the duplex unit.
ADVANCED OPERATION GUIDE 3-7