This is a faceplate for the PT10E or PT24E prototyping board's RM2015S enclosure when the SBC28PC-IR4 board is plugged into it.
This faceplate has labels for RS485 signals on the SBC28PC-IR4 board's screw terminals. If you intend to use CAN bus on your SBC28PC-IR4, you should instead purchase the FPAN-RM2015S-CAN faceplate.