I bought a set of four Thule T-slot bolts which set me back a whopping $6, far less than any other type of mounting kits you can buy. I was intrigued by this attachment method because of its simple elegance. Previously, I had always had either Thule square bars or Yakima round bars, and the Whispbars are my first foray into aero bars with T-slot mounting compatibility. With the aero bars, I did not like the idea of the clamping method, mainly because it looks fugly and clumsy. It came with the stock mounting hardware which is designed to clamp around the cross bar with a combination of metal plates and U-bolts. I picked up a used Sportrack box (Thule's lower end brand, made by Thule) in great shape for $80. My goals in having cross bars are to carry a cargo box and fork mounts (not simultaneously). Since I don't have a pano roof, I wasn't concerned about the tight roof clearance, and I like the tight look of the flush cross bars. I recently installed NOS Whispbar flush aero bars to the factory rails on my GSW.

T slot bolts 14 20 clamping