IBM RT PC Options Installation page 191

8-Port Cable Assembly - RS-422A
The IBM RT PC 8-Port Cable Assembly - RS-422A provides eight
6-pin MODU connectors.
Installing: Plug the 37-pin connector into the desired 8-port
RS-422A adapter; then connect up to eight devices using the 6-pin
MODU connectors on the covered panel of the cable assembly.
Section 6. Communication and Network Adapter Options 6-43