These adapters will allow you to use HID ballasts which were made for D2S/R bulbs with re-based HID bulbs instead. (ie Matsushita or Denso ballast with H1 HID bulbs)
If you already have a set of OEM or D2S specific ballasts and are changing over to something like a Morimoto Mini H1 Projector, there's no need to buy entirely new ballasts to be compatible with the required H1 bulb types.
One side twists into the standard P32-D socket just like a D2S bulb would, and converts the output to be compatible with AMP type HID bulbs.
*It is always recommended that the ballasts and bulbs be naturally compatible rather than using an adapter for the best reliability, but we do make them available for those in need.