What R310RB is on the BOM line
The Mitsubishi R310RB is the IQ-R series PLC expansion module sitting on the line card under PLC expansion modules, addressed by that exact order code and nothing else — no family prefix, no shortened form to specify to the shop floor.
Where this class of part is used
PLC expansion modules of this class are added to a controller rack to bring additional digital or analog channels onto the CPU's I/O table when the base unit runs out of on-board points — the typical use is line-side I/O growth on a production cell or a retrofit that adds sensors or drives without replacing the controller.