E46 Owners: Because of the way the original halogen bulb clips into the housing, an HID bulb won't be a direct swap without these adapters.
Recommended: Check your headlights for a similar looking plastic part socket behind the bulb to identify whether or not you need these. All housings would take H7 bulbs, the original part extends the +/- connector towards the electrical socket.
By Design: Slotted design allows the wiring for the bulb to slide in from the side, and then original clip assembly will hold bulb firmly in place just like stock.