Your Browser is OutdatedWhat is the small set screw used for? — 3 Answers
If you're referring to the 4-40 set screw its because aero threads the rear takedown pin detent channel on their lowers. It's very convenient as you don't have to rely on the endplate to hold the detent and spring in.
It’s to keep the qd pin spring from flying out if you need to take it out it’s made for aero lowers specifically.
Was wondering the same thing and I noticed kns sells a kit with a captured takedown pivot pin and this little set screw can keep that spring from shooting out. Aero also has a threaded bolt release pin which I was surprised was not in this kit, this little threaded set screw definitely is not for that.