Common Thread Mismatches – Important Information

[DPT]

Hi everyone,

This topic comes up from time to time, so I thought I’d put together a post to help clarify the issue.

Unfortunately, several different thread sizes can screw onto each other, creating the false impression of a proper fit. However, in reality, you may only have a fraction of a millimeter of thread engagement, which can lead to your muzzle device—whether it’s a suppressor, brake, or any other attachment—eventually blowing off after repeated use.

Here are the most common thread sizes we encounter:

Imperial Threads:
• 1/2-28
• 1/2-20
• 9/16-24
• 5/8-24

Metric Threads:
• 13x1
• 13x1.25
• 14x1
• 15x1
• 18x1

One of the most frequent mismatches we see is a 5/8-24 muzzle device being screwed onto a 15x1 muzzle thread. The minor diameter (inner hole) of a 5/8-24 female thread is around 14.8mm, meaning a 15x1 thread will only have about 0.1mm of engagement per side. This may hold for one shot or more, but eventually, the muzzle device will come off.

Other common mismatches include:
• A 15x1 muzzle device screwed onto a 9/16-24 muzzle thread
• A 13x1.25 muzzle device screwed onto a 1/2-20 muzzle thread
• Occasionally, a 15x1 muzzle device fitting onto a 14x1 muzzle thread

The above will screw fully home.

The below will only screw a few turns:
• A 9/16-24 muzzle device screwed onto a 14x1 muzzle thread
• A 16x1 muzzle device screwed onto a 5/8-24 muzzle thread

How to Identify Your Muzzle Thread
If you’re not 100% sure what your muzzle thread is, you can measure the outer diameter using a set of vernier calipers. If the measurement is within 0.1mm of a whole metric number, it’s most likely a metric thread.

One exception I can think of is : A 5/8" thread measures close to 15.88mm, which can be confused with the much less common 16x1 metric thread—so be sure to check carefully.

If in doubt, always double-check before installing a muzzle device to avoid damage or safety issues.

Feel free to email or call us directly for further advice, even if you’re using a product that isn’t ours. We’re happy to help.

Hope this helps!

[akaroa1]

Very topical

Also thread gauge sets are very cheap from an Engineering supplier and extremely easy to use. Good for outside and inside threads

A great way of checking the thread pitch

Diameter plus pitch and you can more easily decode what you have and check off against the above info