The Siemens 5SL6350-6BB is a SENTRON 5SL6 miniature circuit breaker — 3-pole, B-curve, rated 50 A at 400 V AC.
B-curve means it trips between 3 and 5 times rated current — 150–250 A for this 50 A unit. That's tight enough to protect lighting and general-purpose socket circuits but won't nuisance-trip on motor inrush the way a C-curve might. Three poles, no switched neutral — the 3P designation means it opens all three phases together but leaves the neutral solid. That's standard for a 400 V three-phase distribution board where the neutral is bonded at the main switch. The 10 000 mechanical switching cycles are typical for this class; you won't wear it out on normal switching duty.
Snap-on DIN rail mount, 3 width units (54 mm wide per the 18 mm/module standard). Height 90 mm. Mounting position any, so it can lie sideways in a tight gland-plate area if you're out of vertical rail. Degree of pollution 2, overvoltage category III — standard for a fixed-installation distribution board. Ambient range -40 to 75 °C, with periodic 55 °C at 95% humidity. The Italy-spec variant means it ships with the standard Italian distribution-board approvals; the sealable toggle feature lets the utility lock the setting.