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Barrel Threading

Barrel Threading


Click Here for special threading notes and facts on barrel threading. Turnaround for barrel threading is around 2 to 3 weeks.

Aquila offers barrel threading services for virtually all situations from just plain threading to machining special adapters.  We single point cut any thread pitch you require and it will be absolutely square and concentric to the bore.  Threads cut on blued barrel will be reblued. Some mounts do not have the proper relief cuts, therefore, we machine tenens on all the barrels we thread for proper fitting.

Aquila has been threading barrels since the 90’s and have encountered some of the most challenging jobs out there.  We have the tooling and the experience to do the job right the first time so that you don't end up with a job like this.

Our thread protectors are all custom machined for the application to match the current barrel and special diameters for autos.  Thread protectors for stainless barrels will be virtually seamless.  For a seamless fit on blued barrels, we refinish the barrel and action, see price list for refinishing charge. Knurled adapters are available on request, no extra charge.

Adapters are needed on some rifles because the barrel is too small for the required thread pitch.  Ex – A barrel with a muzzle diameter of .600 is too small to thread it 5/8 x 24 (.625).  We custom make all of our adapter to fit each application. Additionally, all adapters are installed on the barrel and then finished machined to the final dimensions.  This method reduces the chances of error in concentricity. All of our adapters and thread protectors are made from 416 stainless and Cerakoted to match the finish of the firearm. (See Chart)

We recently were chosen by Gemtech to handle a portion of their barrel threading work and are happy to work with Gemtech’s customers to provide any machining services required.


 If you don't see the specific firearm you need threaded, just ask.

Special Threading Notes: 

Barrel Threading Prices

Additional Services

Special Threading Notes

Threading Info Chart

Chart Description

Common Calibers

These are the most common calibers.  A 5/8 24 thread is used for most 30 cal to 338.

Thread Size

These are the most common thread size and pitches for the calibers listed.

Decimal Equivalent

Simply the decimal equivalency to the fraction, i.e., 5/8 = .625

Minimum barrel Diameter

The required barrel diameter for each thread size.  i.e. 5/8 24 thread needs a .725 barrel diameter.  In most cases, this is not a strict rule.  If the barrel is too small, an adapter can be made to resolve the issue.

Point of Index

This where the shoulder of the silencer actually tightens up against.  Most silencers index off the shoulder behind the threads but some index off the very end of the barrel, the muzzle.

     Repairing Botched Threading Jobs

It pays to have experienced shop like Aquila to perform the job right the first time.   Correcting a botched threading job can be simply cutting of the bad threads and rethreading the barrel or a major machining job.  When cutting the barrel isn't an option, we have other ways to make the repair so that alignment and looks are still perfect. 


The pics below are of a barrel that a shop threaded for one of the local police depts.  They removed the barrel from the receiver and when it was reinstalled, the recoil lug was 1/4" out of alignment and it had deep chuck marks from not being properly secured in the lathe chuck.  All the discoloring and rust was caused by the shop heating the barrel with a torch to remove it. The threads were supposed be 5/8 24 but was somewhere right above 9/16 24.  When the barrel length was cut down, it appears to have be done with a pipe cutter,  metal at the muzzle was mushroomed over the bore, restricting it  by .050.  In ever manner, this job was a complete disaster.

How NOT to thread a barrel

Classes of Threads

Most mounts or flash suppressors have a 2B hole (See description below) and a 3A thread will be too tight for your can or mounts.  If you require “tight” threads, please send the mount so that we can assure it will screw on completely.

There are three established Classes of Thread, designated in the Unified series by adding “A” for screws and “B” for internal threads to show definite limits and tolerances.

Class lB, rarely used, thread is that in which a 1 A screw can be run in readily for quick and easy assembly. The hole is classified as 1 B. The fit is 1 B thread.

Class 2B thread consists of a 2A screw in a 2B hole. This 2B thread has wide application, accommodates plating, finishes, and coating to a limited extent and, therefore, has fair tolerance allowances.

Class 3B thread means a 3A Screw in a 3B threaded hole for applications where tolerance limits are close.

Anatomy of a Threaded Barrel
Barrel threading description

The drawing indicates the major items of a thread.



Axis of a thread: This is an imaginary line running longitudinally through the center of the screw.

Crest: Crest of the thread is the top most surface joining the two sides.

Root: Root of the thread is the bottom of the groove between the two flanks.

Flank: Flank of thread are straight edges which connect the crest with the root of the thread.

Pitch: Pitch of a thread is the distance measured parallel to the axis from a point on a thread to the corresponding points on adjacent thread forms in the same axial plane and on the same side of the axis.

Depth of thread: Depth of a thread is the distance between the crest and root of the thread.

Major diameter: It is an imaginary largest diameter of the thread which would touch the crests of an internal or external thread.

Minor diameter: It is an imaginary smallest diameter of the thread which would touch the roots of an external thread.

Pitch diameter: It is a theoretical diameter between the major and minor diameter of screw threads.

Three Wire Thread Pitch Diameter Measuring

Aquila uses the three wire method, a very common way to measure the pitch diameter of 60° V  screw threads and is the most accurate.  A measurement is taken across three predefined pins or “wires” placed in the thread v usually with a micrometer or calipers.  Once the measurement is taken an accurate pitch diameter can be determined by subtracting a “constant” from the measured dimension to obtain the actual thread pitch diameter.  Additionally, A thread gauge is screwed of the threads to ensure there is no binding.

How to meaure threads
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Threading notes
Botched Threads
Classes of threads
Aatomy of a Threaded Barrel
Thread measuring


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