Will these fit a RAS rail?
They screw into the SIR rail, I forget the thread size/pitch I don't believe it would unless you removed a small section of rail and drilled and tapped it?
Personnaly, I wouldn't do it. Notice in the pic the round section above the threaded area-you would have to take a bit and clear that much area from in between two "peaks" of the rail for the threaded shaft to reach the valley/drilled and tapped area. The area you clear would need to be slightly bigger than the round section, but not so to where the ball detent won't lock it on as wiht the SIR rail.
Sounds harder than it would be, depends on what sling attachment you want. I have both the KAC push button rail attachment and a Deiter CQD hook plate on my different RAS's/Larue
I guess you could find a threaded insert for the existing hole and you would still need to mill out some material as described.