Just a little T Piece for the Bigscreen Beyond Headsets that broke 2 times for me. Without it, you cannot attach any headstrap making the headset not really useable for anything.

Get other pieces from the original CAD files offered by Bigscreen themselves here: https://sketchfab.com/3d-models/bigscreen-beyond-official-cad-data-07b61fc9c1a44662a935b23f88d9f97a