Curve K trips magnetically between 8× and 12× rated current, which is faster than a D-curve on moderate overloads and avoids nuisance tripping on transformer inrush or motor starting currents that a B- or C-curve might catch. That makes it a common choice for protecting inductive loads — contactor coils, solenoid valves, small transformers — where the inrush spike is brief but high.
Snap-on DIN rail mounting means it clips directly onto a 35 mm symmetrical rail inside the enclosure. The 2-pole width occupies two modular units (36 mm at 18 mm per pole), so factor that into the DIN-rail fill count when laying out the panel. No separate mounting hardware or busbar adapter needed for the rail itself.