Yakima tracks - what size T-nut?

The width of the T-nuts are 18mm FYI, I was able to put 8mm T-slot bolts into the tracks for my Front Runner rack, but these were an extremely

Add the SmarT-Slot™ Kit 6 to the SkyBox NX, GrandTour, and CBX Cargo Boxes for an even sleeker profile on T-Slot Crossbars This easy-to-use hardware kit

yakima t slot bolts I have some T-slot style bolts for the front and it seems like that will be easy But the rear looks tricky since the bolt head goes in the

yakima smartslot kit 2 Yakima Roof Basket Parts - T Slot Adapter