The Siemens 3RV2021-1FA10-0DA0 is a SIRIUS 3RV2 motor starter protector in size S0, designed for system protection without phase failure protection. The A-release is set at 3.5...5 A with a short-circuit release of 65 A, using screw terminals and standard switching capacity.
The 3.5...5 A A-release (thermal overload) sets the continuous current range the device protects — sized for a motor drawing up to 5 A full-load. Size S0 is the frame; it dictates the DIN-rail footprint and busbar system it mates with in the panel.
Mounts on DIN rail in the standard S0 footprint. Screw terminals accept copper conductors typical for motor branch circuits up to 5 A. The 102 x 49 x 102 mm package leaves room for adjacent devices in a multi-motor group. No phase failure protection built in — if that's required, you'd step up to the 3RV20x1 variant with the P-release.