If you have one of the old A2 windage knobs for the ARMS#40, ARMS (www.armsmounts.com)will sell you the new style knobs for $18 + $4 shipping.  It comes with some parts you don't need (rear sight windage screw, windage knob pin, etc.), but at least there is not another one of those screwy shaved apetures.

The new knob turns the right way, is slimmer and a darker color.

The item does not appear on their website, but I just e-mailed them using their site, and Mr. Swan wrote me back a few days later.

Just FYI, in case anyone else was annoyed by the old style knob.

I just may have to do this to my rickety old #40!

I really need a #40 for my flat top, dammit!

and an acog! damn ARguy with his pretty purple bushmaster!