I phoned Turk in the King of Prussia store for help with Thule racks. He spent a lot of time answering my questions and it was very productive. Previously, I tried to get the answers I needed online but was unsuccessful. There is nothing that compares to speaking to a live person. There are issues with communication that can't be resolved online. I was under the impression (after using many racks) that all racks clamped onto the fixed roof mounts. Turk explained that some Thule racks are screwed into the roof mount. Major difference. Extremely helpful. Thank you Turk; Rack Attack.