One Pair (2 pieces) of 35w Slim HID Ballasts Our ballasts replace any preexisting aftermarket ballast from an HID conversion kit.  35w and 55w can be interchanged without issue. The ballasts are a universal  and slim fit to connect, plug and play without any modification, to any aftermarket HID bulb.  These are not compatible with factory HID bulbs.  What's Included- Two ballasts per quantity of "1".