The 5SL6606-7CC is a Siemens SENTRON 5SL-series miniature circuit breaker, 4-pole (3P+N), C-curve, rated 6 A at 400 V AC with a 6 kA breaking capacity per EN 60898. The C-curve (tripping characteristic class C) means it holds 5–10× rated current for short overloads — typical for motor circuits, transformers, and lighting banks where inrush is moderate but not negligible. The 3P+N pole configuration switches all three phases and the neutral, so it's the right choice for a 3-phase plus neutral distribution board where you want neutral isolation. Rated for 400 V AC phase-to-phase, with a multi-phase maximum of 440 V AC. The DC rating is 72 V maximum.
That 6 mm difference is the front toggle and marking area. For a crowded enclosure, the 70 mm rail depth is what you plan for gland-plate clearance and wire-bend radius. This is a dry-indoor-panel breaker, not a washdown or outdoor enclosure part. That covers unheated utility rooms and outdoor-adjacent cabinets in most climates. Halogen-free and silicon-free construction — important for fire-safety zones (tunnels, high-rise risers, data centers) where halogen off-gassing is a life-safety concern.