Roof rack installation
 

I bought my 2013 Tahoe without a roof rack and am now adding an original GM one. I bought all the parts and am puzzled as how to attach the roof rack to the roof.

The Tahoe roof has 5 hexagon shaped (=6 corner) holes on the left and right side. These are pre-drilled at the factory to fit the roof rack. (since we bought ours without the rack, the holes were filled with rubber stops that are easy to pop out)

The GM roof rack comes with hexagon shaped nuts. These slide right into the pre-drilled holes on top of the Tahoe. The roof rack side rails then go on top of these and from the top, a bolt attaches the side rails into these nuts that stick in the Tahoe roof.

However, before I go attaching anything heavy to the roof rack: how are these nuts that simply stick into the roof without any 'connection' to the Tahoe's roof keeping the roof rack on the Tahoe? Am I missing a part that holds/clamps the nuts in the roof?

Welcome to the forum.
The factory stock roof rack uses Wellnuts (https://en.m.wikipedia.org/wiki/Well_nut) in the roof itself. Wished I'd known you were looking for one because I've got one I could have sold you really cheap.

Thanks for the welcome!

These are the nuts that came with it: https://www.ebay.com/itm/202155950681
They fit perfectly in the hexagon holes in the roof and have a small rubber liner to keep the rain out (I guess).

Are these similar / the same as the factory parts?

Further research and I learned something new: "rivnuts" or "well nuts" or "rivet nuts" are something I'd never heard of. I learned that there are tools out there to install these in an easy manner. However, I just spent a few hours going to Home Depot, Lowes, O'Reilly's, Napa, Harbor Freight, ... and none of them carry a rivnut tool. (although most do carry a regular riveting tool)

It's Sunday today so I'll see if I can find a car mechanic tomorrow who can install the 10 rivnuts that the roof rack requires. Or I could order a tool from Amazon ... but it's priced quite steep considering I'll only use it once for the roof rack.

You are correct, those are rivnuts or something very similar. They act similarly to a pop rivet and that the tool pulls the threaded portion up against the back surface the roof to retain the rivnut.

2018 Suburban roof rack
 

The roof rack on the 2018 Suburban (or Yukon) is flush mounted to the roof of the vehicle. There is no space between the side rails and the roof of the vehicle for a hook or rope to pass. Can the roof rack be modified to create some space? Can you drill into the flush-mounted roof rack without completely destroying the integrity of the rack? I'd like to be able to use ratchet straps with hooks from side rail to side rail like you could on older models.