This is required to extract the APS shell properly, I personally have it in steel, however the plastic version should work fine.
Only one is required for the set.
Big thanks to James Smith on YouTube for creating this tutorial video on the installation and testing of this kit.
*09 July 2021 update: despite many of these being sold and worked fine since 2015, yesterday I received a complaint for the first time that the metal one had fitment issue due to tolerance shift during the metal casting phase. So while so far all but one order has had issue, if you would like this piece in metal (my personal one is also in metal), please be aware there is a small chance you will have to file excess to fit should the roll of the dice be not in your favor. Thanks!