Aero's Fix-It Kit gets you the most commonly lost parts to finish your build. All parts in the Fix-It kit are compatible with AR15, M4E1 and M5 builds. Kit includes- 4- Takedown Pin Detents, 4- Takedown Pin Springs, 2- Bolt Catch Roll Pins, 2- Trigger/Hammer Pins, 2- Safety Selector Springs, 2- Safety Selector Detents, 2- Buffer Retainers, 2- Buffer Retainer Springs, 2- Disconnector Springs, 2- 4-40 Set Screws (for threaded takedown pin detent hole) and a threaded Roll Pin. Made in the USA.