The Barox PD-DIN-KIT-VDSL is a mounting set for fitting compatible Barox equipment on a DIN rail. The manufacturer identifies it as a mounting plate and lists it as an optional installation accessory for the PD-VDSL-MI1G Ethernet extender.
The set is ordered separately, so it is not part of the extender’s included accessories. It provides a way to mount the referenced extender on a rail rather than use it as a tabletop unit. The manufacturer document does not specify the plate’s dimensions or material.