The Siemens 3VU2916-0B is a door-coupling rotary mechanism designed for the 3VU2.1, 3VU2.2, and 3VU2.3 series of circuit breakers. This is the mechanical interface that lets you operate the breaker handle from outside the enclosure door, keeping the door closed while switching.
Mounts to the enclosure door and couples to the breaker's rotary operating mechanism. Panel builders will need to align the shaft extension with the breaker's drive coupling before securing the door plate — the kit includes the rotary handle, shaft, and door interlock provisions.