The Siemens 3RT1945-5AJ11 is a replacement coil for the 3RT series contactors. It's the part you swap when the coil burns out or the contactor gets a new control voltage. Listed at 0.27 kg, it's a straightforward swap-in — pull the old coil, clip in this one, torque the terminals, and the contactor's back on the line.
What the weight tells you
At 0.27 kg, this coil is sized for the 3RT frame. That's a shipping and handling number, not a selection parameter — but it does tell you the magnetic core and winding mass are consistent with the 3RT contactor's pull-in force curve. If you're swapping coils in a panel, the weight confirms it's the right physical size for the contactor base.
Category note
This is a contactor coil, not a filter choke. Search under Contactors, not Inductors.