The Siemens 5SJ4145-7HG40 is a SENTRON miniature circuit breaker (MCB), 1-pole, C-curve, rated 45 A at AC (also 45 A at 40 °C ambient). It is the standard panel-protection building block for branch circuits in industrial control cabinets — mechanical engineering and industry applications per the listing.
Rated 45 A at 30 °C and 40 °C, derated to 43.7 A at 45 °C, 42.8 A at 50 °C, 41.7 A at 55 °C, and 41 A at 60 °C. Maximum DC voltage is 60 V, so it's fine for 48 VDC control circuits but not for a 125 VDC battery bank. Overvoltage category 3 and pollution degree 3 mean it's rated for the fixed-installation environment inside an industrial enclosure.
Width is 18 mm (one modular unit), depth 70 mm, height 90 mm. Terminals are combined (top and bottom) — not tunnel type — so you land a ring or fork lug. Terminal tightening torque is 3.5 Nm for copper conductors rated 60/75 °C. Sealable, halogen-free, silicon-free. IP20 with connected conductors, IP40 in the handle area.