Those are known as grip fins and are made by a lot of different companies now. Pics https://www.google.com/search?q=grip+fin&rls=com.microsoft:en-US:IE-Address&rlz=1I7GZGN_enUS478&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjP1ublw6bRAhXFjlQKHa2fDo8Q_AUICSgC&biw=1366&bih=644 The idea is that it doesn't allow you to wrap your thumb around the grip and thereby should be CA compliant with the definition of a pistol grip including being able to (paraphrasing) wrap your hand around the grip where-as the web of your hand is lower than the top of the trigger. IMO, it not effortless. Its like trying to grab a soda can with out using your thumb. IMO, a better option for the AR15's is to covert to a different stock with an Exile Machine converter or go to a different style stock such as from Thordson. (Note, I am in no way affiliated with Exile or Thordson. IMO, they are one of the better options. Also not, Exile has a stock convertor that a CA DOJ agent testified in court that it makes the rifle not fit the fit the definition of having a pistol grip) I would expect that the rifle makers will start offering featureless AR of their own; hopefully.