The Siemens 3RT1326-1AK60 is a SIRIUS power contactor in size S0, with four normally-open main contacts rated for 11 kW at AC-2 duty on 400 V. That AC-2 rating means it's built for slip-ring motor starting — the kind of load where you need to handle moderate inrush and make/break under load repeatedly.
The 4 NO main contacts give you four independent poles — handy if you're switching a motor plus a separate load or need to break multiple phases cleanly. The mechanical life is 10 million cycles, so it's not a throwaway part — expect it to outlast the cabinet in most conveyor or hoist applications.
Main terminals accept solid or stranded wire: 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), and up to 2x 4 mm² max; AWG equivalents go from 2x 20-16 down to 1x 12 for the main circuit. Auxiliary contacts use the same screw-terminal range. For short-circuit coordination, type 1 requires a 63 A gL/gG fuse, type 2 requires 35 A — that's per IEC 60947-4-1, and it's what you hand to the panel builder so they don't oversize the protection and lose the contactor in a fault. The coil operates at 50/60 Hz with a tolerance of 0.8 to 1.1 times rated voltage, so it holds in on a saggy line.