# Are all AR-15 barrels threaded 1/2x28?

**Verdict: It depends**

No — most 5.56 ones are, but .300 Blackout barrels on the same platform are usually 5/8x24. Measure or check the maker before ordering.

1/2x28 is the standard for .223 Remington and 5.56 NATO, and that covers most AR-15 barrels sold. It is a strong convention rather than a property of the platform, and the exceptions sit on rifles that look identical from the outside.

The one that catches people is .300 Blackout. It runs a 5.56-size upper — same bolt, same magazines — but the muzzle follows the .30-calibre convention at 5/8x24. Buying a muzzle device for "my AR-15" is exactly how the wrong thread pitch arrives in the post.

- **.223 / 5.56** — 1/2x28, near-universally
- **.300 Blackout** — Usually 5/8x24, occasionally 1/2x28
- **Large-frame .308** — 5/8x24
- **The reliable move** — Check the maker’s spec for your barrel

> **Caution:** Thread pitch cannot be judged by eye, and a barrel that came threaded from a manufacturer is the one to ask about rather than measure badly. Where a barrel’s history is unknown, a thread pitch gauge costs less than a muzzle device.

## Sources

- [AR-15 thread pitch — the common pitches and what they sit on](https://catoutdoors.com/ar-15-thread-pitch/)
- [Common barrel thread patterns — 5/8x24 on .300 Blackout](https://www.silencercentral.com/blog/silencer-common-barrel-thread-patterns/)

## More on barrels and muzzle devices

- [Will a 1/2x28 muzzle device fit a 5/8x24 barrel?](https://www.tactgpt.app/answers/muzzle-device-thread-pitch-mismatch.md)

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Last checked 2026-09-03. TactGPT can make mistakes. Always check important info for accuracy. The information it provides is intended for educational purposes only. It does not give legal advice; verify any laws cited. Always follow all applicable laws and safety guidelines.

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