This is a faceplate for the IOR5E relay board enclosure when the SBC28PC-IR2 board is plugged into it.
This faceplate has labels for RS232 signals on the SBC28PC-IR2 board's screw terminals. If you intend to use CAN bus on your SBC28PC-IR2, you should instead purchase the FPAN-IOR5E-CAN faceplate.