It's a phased-out product — the successor is the SIRIUS 3RT2 series, so if you're holding a BOM line with this code, that's the cross-reference you need for a new-design replacement. The coil operates across 0.8 to 1.1 times the rated voltage at 50 Hz, which means it pulls in reliably down to about 88 V and holds through line sags up to 121 V — a useful tolerance for industrial control circuits with shared transformer loads.
This coil mounts onto SIRIUS Size S2 contactors — the 3RT2 series frame that uses screw terminals for the coil connection. If you're swapping a failed coil in an existing panel, verify the contactor frame size and the coil voltage; the 110 V AC 50 Hz winding is specific to that supply, and a 60 Hz or DC coil won't interchange without changing the control transformer or rectifier.