Yes a special adapter is required. The ones on my car have a spline type configuration. The adapter slides into the spline and has a hex head so that a conventional lug wrench can be used. I bought a set of lug nuts that have an internal hex since I thought they might look better on an old car, but the adapter that would be used to install/remove is too short. I haven't spent the time to try to figure out a solution. The wheels would go on the car before I relieved them, but was tight to get them lined up and all the lug nuts started. My buddy has a Bridgeport mill, so we used that to mill the reliefs. No problem getting the wheels on and off now.