PF-040 can be purchased with the optional takedown/pivot detents (4) and springs (3) kit. The odd numbers of included components probably deserve some explanation. Even for experienced AR builders, it's not uncommon to launch the pivot pin detent into the twilight zone. It's also fairly easy to bend the take down pin detent spring during installation of the end plate and castle nut. So the optional detents and spring kit includes 4 detents and 3 springs to preempt losses and damages. If you don't end up needing and using all of them at once, the kit is reasonably priced, and always good to have on hand to grow into another AR
PF-040 may not work "PDW" stocks that have bars overlapping the take down pin holes.
PF-040 may be shipped with the old PWA-040 instructions card, the name under which it was sold up till Feb of 2019. The pins are identical, Forward Controls acquired the rights to the pins in Feb. of 2019.