These adaptor plates giveyou the ability to attach 2 Thule slottedLoad Bars or Aero Bars to a Front Runner Slimline II Roof Rack. If you currently own Thule Accessories and would like to use them with a Front Runner Slimline IIRoof Rack, you can use your Thule load bars or Aero Barsto mount your accessories (e.g. Bike Mounts or Kayak mounts) to the rack. If you currently own Thule Load Bars on your vehicle,you can also use these adapter plates to mount a Front Runner Slimline II Roof Rack Tray to your load bars. Works with both theSLOTTED-SQUARE and AERO Thule Load Bars. This adapter plate DOES NOT work with theThule rectangularload bars that do not haveslots (ie. the basic Thule load bar found in the USA.) 3CR12 stainless steel. Black powder coated. Mounts onto individual slats via the T-slot system. T-slot bolts included. Pre-cut fitment holes.