These adaptor plates give you the ability to attach 2 Thule slotted Load 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 II Roof Rack, you can use your Thule load bars or Aero Bars to mount your accessories (e.g. Bike Mounts or Kayak mounts) to the rack. Works with both the SLOTTED-SQUARE and AERO Thule Load Bars. This adapter plate DOES NOT work with the Thule rectangular load bars that do not have slots (ie. the basic Thule load bar found in the USA.) Steel. Black powder coated. Mounts onto individual slats via the T-slot system. T-slot bolts included. Pre-cut fitment holes.