[sepulchrave]

I found one from an old RG with the indent but the screw size was wrong.

What does this mean please?

You want a 43mm locknut with the truss rod clearance cutout, by far the best thing to do is just order a new one complete with all fasteners and fixings.

That one is wrecked and looks like it's only 42mm.

 

[sepulchrave]

That RG440 must be an '87 because it has the RG headstock rather than the RS headstock shape, therefore it must be 16" radius and that RG locknut that you have with the cutout should be just right, you just need the correct metric screws for it.