Atari 2600 controller?

I picked this up at salvation army store few weeks ago.  I know its a lot but even ebay a working controller with shipping nothing less.  Anyhow there was no model number. So is this CX-10 or CX-40??  And which came first 10 or 40??  Which was the original??

http://mvvg.blogspot.com/2013/09/atari-2600-controller.html