You can create a rectangular sketch above the part and extrude it through the channel as a cut. I, however, reccomend this library and add in for fusion 360
@thirddegree , @andrewef2000 , and I are proud to announce the release of the VEX CAD Library for Fusion 360! This library is based on the hard work done by the contributors of the VEX CAD Inventor Library .
This parts library includes a number of parametric parts such as adjustable length C-channels and gears with swappable inserts that can be edited using our custom add-in. The add-in is not required to use this library but is highly suggested for your ease …