Probably the alloy used. Might also have something to do with the chemical composition of the acid bath or ano bath.
I know T6061 anodizes clear, you can’t tell it’s there by sight but it still offers mechanical lockout at the tail cap by breaking the connection from the clean edge with a slight unscrew of the cap.
I already expressed interest in Post #41 but I just wanted to add that if the price is right, I may want as many as three units. I’m curious when we will get more details here.