It's a supplementary protector per UL 1077, meaning it's built for branch-circuit protection inside equipment, not as a main service disconnect.
What Trip Curve K means for your load
Trip Curve K is the middle ground between a B curve (light commercial loads) and a D curve (high-inrush motor circuits). The thermal-magnetic mechanism inside gives you a thermal trip for sustained overloads and a magnetic trip for fast short-circuit clearance.
Where it goes and how it fits
The finger-safe terminals accept up to the wire range you'd expect for 50 A (typically #14–#4 AWG copper). It's a panel-mount part: you'll see it inside a control cabinet feeding a motor starter, a power supply, or a heating load. No special mounting hardware needed, just a slot on the rail and a screwdriver for the terminals.