The Siemens 5SL6406-6 is a SENTRON miniature circuit breaker, 4-pole, B-curve, rated 6 A at 400 V AC with a 6 kA breaking capacity per both EN 60898 and IEC 60947-2. It's the kind of part you snap onto a DIN rail in a residential or light-commercial panel and forget about — until a fault happens, then it clears the circuit cleanly. Rated 6 A at 30 °C, it derates to 5.64 A at 40 °C and 5.04 A at 55 °C — so if your panel runs hot, you need to account for that when sizing the branch circuit.
That's standard for most residential and light-commercial panels where the prospective fault current doesn't exceed 6 kA. If your installation has a higher available fault current (say 10 kA or 25 kA), this isn't the breaker for that spot. The -40 °C to 75 °C operating range covers unheated utility rooms and outdoor enclosures in most climates. The 10 000 mechanical switching cycles is typical for this class — it's not a contactor meant for daily load switching, but it'll handle occasional on-off operation for isolation and testing without wearing out early.