The K characteristic means it's designed for motor and transformer circuits where inrush currents are higher than resistive loads — the magnetic trip threshold sits between 8 and 12 times rated current, so it holds through the start-up surge without nuisance tripping on a 20 A motor branch.
Snap-on DIN rail mounting for standard 35 mm rail. Three-pole form factor takes up 3 module widths (about 54 mm) in the panel.