The Siemens 3RV1985-5GA0 is a set of phase barriers, 100 mm long, designed for the SIRIUS 3RV1 family of motor-protective circuit breakers. You get 8 units per pack, intended to maintain phase-to-phase and phase-to-ground clearance when you stack breakers side-by-side on a DIN rail. This is a panel-builder detail that keeps the assembly compliant with IEC 60947-1 creepage distances without having to gap the breakers apart.
The 100 mm length covers the full depth of the breaker body. No re-termination is needed — the barriers fit around the line and load conductors. If your panel was specified around a 3RV2011-0BA20 or similar S00/S0 frame, the 3RV1985-5GA0 is the correct accessory for maintaining isolation between units.