Can anyone tell me what the bottom bracket with slotted holes are for on my cargo side rails?

[2015MustangGT]

 

[mikeru82]

I don't know for sure. My rails don't have those. I'd assume that bed accessories would mount there though.

 

[2015MustangGT]

I don't know for sure. My rails don't have those. I'd assume that bed accessories would mount there though.

It’s also slotted on top. Guessing the same, must have a purpose, but the dealership couldn’t tell me.

 

[Ramfirsttimer2019]

I am not sure, but I would love to have your rails vs mine. I have the black ones that come with the factory tonneau cover and bought an aftermarket cover (bakflip F1), but it fits only on the silver ones you have. Want to trade rails? you can have the black ones and the tonneau cover. (I'm in CT)

 

[Fatherof3]

I’m just guessing as I really don’t know , but maybe it’s just to allow water to drain instead of puddling in the track .