Add the SmarT-Slot™ Kit 5 to the TopWater™ box for an even sleeker profile on T-Slot Crossbars. This easy hardware kit replaces the standard mounting hardware, and directly attaches into a T-slot channel on your crossbars. It works with all Yakima® T-slot crossbars as well as most other T-slot crossbars. (NOT Whispbar HD)