This breaker carries three breaking-capacity ratings depending on the standard you're designing to: 10 kA per EN 60898 (the household / commercial standard), 20 kA per IEC 60947-2 (the industrial standard), and 5 kA per UL 1077 / CSA C22.2 No. 235. If your panel is UL-listed, the 5 kA UL 1077 rating applies — that's the supplementary-protector limit, not the branch-circuit rating. For a UL 489 listed branch breaker you'd need a different SKU.
The 18 mm width (1 width unit) means it takes up one slot in a standard distribution board. Terminals accept solid or stranded copper from 0.75 mm² up to 35 mm² — that's a wide range, so you can land a 6 mm² feeder or a 25 mm² subfeed without adapters. Ambient temperature range -25 to +55 °C, storage -40 to +75 °C.