What is the Thule Pro Bar for T Slot Tonneau Covers?

It uses a T-slot track system that lets you fit crossbars across the Hard tonneau covers don't have this issue, but again, that

2021+ Ford F150 - Tonneau Cover with t-track rails?

tonneau cover with t slot Versatile with Trax Rail System and T-Slot accessories Easy to Track-mounted racks: Some racks are secured directly to the built-in tracks on

graphics card with m2 slot Features Designed to work with tonneau covers equipped with a T-slot: UltraGroove & Retrax XR Channel Rails, but works with any T