Supports a card inserted into the vertical riser slots on the Corsair 4000D. The holes are aligned for the front vertical slot and a LINKUP - Ultra PCIe 4.0 X16 Riser Cable. There's a mounting hole that will get attached to the case to keep the bracket from moving back and forward. 

The holes that hold the Riser cable in are threaded for up to an M3 x 7mm screw (I found 5mm works best).

This is exceptionally handy if you have a heavy graphics card (like the new RTX 30xx series).