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What is the one small grub nut for? No documentation of any kind provided. — 1 Answer

by Lee, from PA, United States Asked on May 6, 2021

Name Aero Precision AR-15 Lower Parts Kit w/Magpul MOE (4.3)
$110.00 $98.99 Save 10%
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Answered by Aero Precision USA, Manufacturer from WA, United States, on October 08, 2021

That is the 4-40 set screw. It is designed to secure the takedown pin detent and spring in place since the channel is threaded on our M4E1 and M5 lowers. Although not necessary to use, it is recommended. You will need to trim away ~1/4 of an inch from the takedown pin spring to accommodate the use of the 4-40 set screw.

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Last updated 2025-11-12 UTC.