They are D2R... not specific to any halogen type... they have to be fit into halogen housings, which is pretty easy. With your headlights, you can take the "flange" off a halogen H4 bulb and secure it to the base of the HID bulbs... then the whole thing just mounts in your headlights like the halogen bulbs did.

The ballasts are really small too, makes it easier to find a place to mount them!