I'm probably using incorrect terms.

I know the barrel nut is installed, and the rail is over top of it. The base of the rail where it meets the upper has a section where two hex screws secure it.

But I got the handguard/rail dirt cheap and idk if it's intended to tighten until the metals wings clamp together, or if there is a missing piece that is supposed to go between them, like a washer or something else to provide tension.