The Siemens 3RH1921-1DA11-0KR0-ZX91 is an auxiliary switch block from the SIRIUS 3RH1 series, providing 1 normally-open and 1 normally-closed contact. It mounts on the side of Size S0 through S12 motor contactors, with a 10 mm width and screw terminals, following EN 50012 mounting dimensions. This is a phased-out product — the official successor is the SIRIUS 3RH2 series.
The lifecycle stage is listed as current, but the description explicitly marks it as a phased-out product with the successor being the SIRIUS 3RH2 series.
The 1 NO + 1 NC contact configuration is standard for signaling contactor position or interlocking in motor control circuits. The EN 50012 profile ensures mechanical compatibility with the S0–S12 contactor frame — a panel builder can snap it on without modifying the existing DIN-rail layout.