What goes in this hole?

[Diver6]

Just cause theres a hole doesn't mean you have to stick something in it!! Thats what my wife told me!

[Donstar]

I believe that would be used to lock in an item placed in the stake pocket.

Drop in liners are usually installed with self tapping screws. These holes allow you to secure wooden stakes when building up the sides of your truck! They are now more commonly used for other accessories.

[cbrsilv15]

I have a Lo Pro QT tonneau cover and the clamp bolt runs through that hole. The plastic plug was tossed.