Help identifying various attachment points in the bed.

[fordgt]

There are six 6mm threaded inserts (3 on each side) basically up under the rails. They go from the back forward, starting above the bed lights and spaced out approximately every 8 inches.
my other question is, what are the 4 plastic plugs in the “pillars” of the bed at each corner?

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[PhoenixRanger]

I'm guessing they are pre-drilled for the Factory Bed Track and Cleat Cargo Management System. The plastic plugs are probably for wires/electrical for a camper shell.