Bronze Sphere is a Quest item in Torment: Tides of Numenera.
This is a fist-sized bronze sphere that you removed from a transdimensional space inside your head. Its surface is covered in interlocking spirals. Interacting with the sphere allows you to swap companions out on the fly, making it an essential item to procure before leaving Sagus Cliffs.
- Buried Crossroads: Removed from your head using the mirrors.
Behind the scenes
It is probably a reference to Planescape: Torment's Bronze Sphere, a quest item central to the first part of the game.