How to Thread an AR-15 Rear Takedown Pin Detent Hole

Published on May 31, 2026
Duration: 5:22

This guide details how to thread the rear takedown pin detent hole on an AR-15 lower receiver using a 4x40 tap and a set screw. This modification allows for easier removal of components like the end plate and buffer tube without losing the rear takedown pin spring and detent. The process involves careful tapping with cutting oil and a specific technique of rotating and backing out the tap to create clean threads. It also covers trimming the takedown pin spring to accommodate the set screw.

Quick Summary

Threading the rear takedown pin detent hole on an AR-15 lower receiver allows for the use of a set screw to secure the spring and detent. This modification simplifies component swaps, preventing lost parts when removing the end plate or buffer tube. Essential tools include a 4x40 tap, tap wrench, and cutting oil. After threading, trim the takedown pin spring by about 1/8 inch.

Chapters

  1. 00:00Introduction & Benefits of Threaded Hole
  2. 00:07Why Thread the Rear Takedown Pin Hole?
  3. 00:28Tools and Materials Needed
  4. 00:34Understanding Taps (Plug vs. Tapered)
  5. 00:46Tap Material (High Speed Steel)
  6. 00:53Tap Wrench Options
  7. 01:05Cutting Oil Importance and Alternatives
  8. 01:20Set Screw Details
  9. 01:30Preparing the Tap Wrench
  10. 01:38Initial Setup and Cleaning
  11. 01:46Applying Oil and Starting the Tap
  12. 02:03Threading Technique: Rotate and Back Out
  13. 02:27Removing the Tap and Cleaning
  14. 02:46Checking Thread Depth and Flushness
  15. 02:53Key Principles: Straightness and Oil
  16. 03:02Trimming the Rear Takedown Pin Spring
  17. 03:17Conclusion & Support the Channel

Frequently Asked Questions

What are the benefits of threading the rear takedown pin detent hole on an AR-15?

Threading the rear takedown pin detent hole allows you to use a set screw to hold the spring and detent in place. This prevents them from shooting out or getting lost when you remove components like the end plate, castle nut, or buffer tube, simplifying maintenance and reassembly.

What tools are essential for threading an AR-15 rear takedown pin detent hole?

You will need a 4x40 high speed plug tap, a T-handle tap wrench (0-1/4 inch), cutting and tap oil, and a 4-40 by 1/8 inch socket set screw. A vise is highly recommended for stability.

What is the correct technique for using a tap to thread a hole?

After applying oil, start the tap straight and turn it for a full rotation, then back it out by half a turn to break the chips. Repeat this process, maintaining straightness, until the desired thread depth is achieved.

Do I need to modify the rear takedown pin spring after threading the hole?

Yes, after threading the hole and installing the set screw, you will likely need to trim about three to four coils (approximately 1/8 inch) from the rear takedown pin spring. This compensates for the space taken up by the set screw.

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