What you're looking at
This is a Siemens SENTRON 5SJ6440-6 miniature circuit breaker — 4-pole, B-curve, 40 A, 6 kA breaking capacity per EN 60898, rated for 400 V AC supply.
Solid and stranded conductors both accepted 0.75 to 25 mm². That's a generous range — covers everything from 1.5 mm² control wiring up to 6 mm² or 10 mm² feeder tails. 70 mm installation depth leaves room behind the DIN rail for cable bends. Sealable (padlockable) for lockout/tagout. Touch protection built in — no exposed live metal when the breaker is off. Vibration rated at 50 m/s² from 25 to 150 Hz and 60 m/s² from 10 to 150 Hz per IEC 60068-2-6 — it'll hold up on a machine base or near a motor.