Corona Grading Ring

Is this what you mean? If so, it's the same in the US.

A corona ring, also called anti-corona ring, is a toroid of (typically) conductive material located in the vicinity of a terminal of a high voltage device. It is electrically insulated. Stacks of more spaced rings are often used. The role of the corona ring is to distribute the electric field gradient and lower its maximum values below the corona threshold, preventing the corona discharge.

Corona rings are often seen on van de Graaf generators, electrical insulators, Cockcroft–Walton generators, particle accelerators, high voltage bushing terminals, and other high voltage equipment.