That matters when you're squeezing a retrofit into a crowded backplate. Overall dimensions: 73 mm deep, 45 mm wide, 70 mm high.
The 3RH2131-2KF40 carries three normally open instantaneous contacts. The switching capacity depends on the voltage you're switching: at 110 V rated value it handles 3 A, at 230 V it's 10 A, at 400 V it drops to 3 A. That 10 A at 230 V is the sweet spot for most control-circuit loads — solenoids, contactor coils, indicator lights. At 24 V it's 10 A; at 60 V it's 4.7 A. The arcing time sits at 10–15 ms, and the mechanical life is 30,000,000 operations typical — that's decades in normal cycling service. The coil closing power at DC is 2.8 W, so it's light on the control transformer.