How to Install a Takedown Pin Using a 4-40 Set Screw

If you have purchased a lower receiver from Aero Precision (M5*, EPC, AR15 Gen II or M4E1), you have the option to install your takedown pin using the 4-40 set screw that is found in any Aero Precision lower parts kit. Installing your takedown pin this way can help streamline the assembly process and any future modification or maintenance.

*Note: The installation of the takedown pin on an M5 Lower Receiver varies from the AR15, M4E1, and EPC.

To do this install you will need 2 tools:

• Wire Cutters
• .050” Hex Wrench

First, you will want to set your takedown pin into your lower receiver as you normally would, then drop the detent, and detent spring into their channel ensuring the detent is engaged with the channel in the takedown pin. From there all you need to do is trim the takedown pin spring just above flush with your lower receiver using wire cutters and install the 4-40 set screw using your .050” hex key.  Tighten the screw until it is completely flush with the lower receiver. If your takedown pin feels too tight, you may have not removed enough coils from the takedown pin spring (take care not to trim it flush or below with your lower receiver).

Once you ensure proper function your takedown pin is installed and you can continue assembling your lower receiver as you normally would minus these components!