How do I spin a part that is welded to another part?

Hello, I want to have a constantly spinning part but it has a parent that is also a part that is welded to the part I want to spin.

I have highlighted what I want to spin in RED and what I don't want to spin in BLUE Image

I currently use this script but it spins both the parts.

while true do
	script.Parent.CFrame = script.Parent.CFrame * CFrame.fromOrientation(0,0.4,0)
	wait(0.01)
end

You can't spin one part by itself if both parts are welded; they'll spin in unison. You can make the surface of an anchored part a Motor and attach the other part to that Motor (the other part must be unanchored). (Use RotVelocity to control the motor speed if you do this.)