The ABB XT5LQ340ABFF000XXX is a XT5L 400 breaking part, 3P F F UL/CSA. This is the interrupting portion for a three-pole XT5L 400 frame molded case circuit breaker — the part that actually clears the fault. If you're rebuilding a breaker in the field rather than swapping the whole unit, this is the subassembly you need.
What the breaking part covers
The UL/CSA marking means it carries the necessary approvals for North American panel builds — no separate UL listing chase required for the replacement part.