FAQ: Guide to Muzzle Threads

“Threaded Barrel Accessories” have one thing in common: they thread onto the muzzle end of your firearm’s barrel. Because of this, it is critical to know the thread pattern for your firearm’s muzzle so you can choose the correct muzzle accessory.

Thread Basics

There are several aspects of threading which are important when choosing the correct muzzle accessory for a particular purpose. These are:

• • Thread Pitch
  • Thread Handedness
  • Gender

Thread Pitch

Thread pitch refers to how many threads are present along the axis of the threaded item (in our case, the “threaded item” is either the barrel of your firearm or the muzzle device).

Thread Handedness

Thread handedness refers to the direction of the threads. Normally, threads are “right-handed” (RH) such that tightening requires rotating in the clockwise direction (“righty tighty, lefty loosy”). Alternatively, some threads are “left-handed”  (LH) such that tightening requires rotating in the counter-clockwise direction. If the handedness of a thread is unspecified, it is typically safe to assume it is right-handed (RH).

Thread Gender

Finally, threads can be described by their gender. “Male” threads are on the outside of the threaded item while “female” threads are on the inside. As an example that most of us are familiar with, a bolt has male threads while a nut has female threads.

Thread Standards

There are numerous standards for threading, only a couple of which will be important for our application of firearm barrels and muzzle devices.

Unified Thread Standard (UTS)

Unified Thread Standard (UTS) threading is divided into several categories based on the fineness or coarseness of the threading. UTS threads are referred to using the thread diameter in fractional or decimal inches along with the “threads per inch“.

Unified Coarse (UNC)

Unified Coarse (UNC) threads encompass threads having relatively coarse thread pitch, hence the name. UNC threading is not common for muzzle threading.

Unified Fine (UNF)

Unified Fine (UNF) threads, as the name implies, have threads with a smaller or “finer” pitch than Unified Coarse. UNF threads are described by their nominal diameter and “threads per inch”. Examples of UNF threads include 1/2″×20, 5/8″×18, and 3/4″×16.

Unified Extra Fine (UNEF)

Unified Extra Fine (UNEF) threads have yet smaller or finer thread pitch than Unified Fine (UNF). Examples of UNEF threads include 1/2″×28, 5/8″×24, and 3/4″×20.

ISO Metric

ISO Metric threads are described by their diameter and pitch (pitch being the distance between individual threads). Hence, a M16x1 thread has a 16mm nominal diameter and 1mm thread pitch. Examples of ISO Metric threads include M14x1, M16x1, and M18x1.

What Thread Does My Muzzle Have?

Unfortunately, muzzle threading is not standardized. Typically, the best way to know the muzzle threading for your firearm is to consult your owner’s manual (if your firearm came threaded from the factory). If your firearm is older or purchased used, that may not be possible. Below are some rough guidelines on what your muzzle threading might be in those situations.

US-Made Pistols

9×19 and .38 Super: typically 1/2″×28 RH

.40 S&W and 10mm: typically 9/16″×24 RH

.45 ACP: typically .578″×28 RH

Foreign Made Pistols

5.7×28mm: 10×1 RH

9×19mm HK, M&P, SIG Sauer: M13.5×1 RH

.40 S&W HK: M14.5×1 LH

.45 ACP HK USP, HK45T, Kriss: M16×1 LH

.45 ACP HK Mark 23: M16×1 RH

The above list, as you might imagine, is nowhere near exhaustive of the possibilities of barrel threading. If you don’t have a manual for your firearm, can’t find a manual with an internet search, have an older firearm, or your firearm was custom threaded and you’re unsure of the actual threading there are a couple options to determine the actual threading that aren’t terribly expensive:

1. 1. buy a nut at your local hardware store with the threading you suspect for your barrel; most hardware stores will carry the more common thread pitches
   2. buy a “thread gauge” from your local hardware store or online (Amazon has several at reasonable prices: Amazon “Thread Gauges”)

For those firearms with unusual muzzle threading, our online store provides a quick and easy “Firearm Specific” product filter to assist you in selecting the correct thread adapter, thread protector, or muzzle brake. Just find your firearm in the “Firearm Specific” list and click the adjacent checkbox to see all products having the appropriate threading for your firearm.

If your firearm isn’t listed, it probably has “standard” muzzle threading which follows the above list of common muzzle threadings.