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Thread Concentricity GO/NO-GO Gage for 1/2-28 5.56mm


Product Description

This gage will allow you to check whether the 1/2-28 threads on a 5.56mm weapon are concentric with the bore. Most sound suppressor manufacturers list 0.003" (3 thousandths of an inch) as a standard tolerance for thread concentricity. This tool will allow you to see if your barrel is within this specification. If the pin does not slide freely into the barrel, this means your threads are out by at least 0.003”. This could cause a sizable point of impact shift and possible baffle strikes.

  • Simply hand-tighten the knurled body section onto your 5.56 weapon.
  • Drop the bore alignment pin into the hole on the knurled body.
  • Use a light touch to insert the pin. Very little/no force should be needed.
  • If the threads are within 0.003, the pin should slide freely all the way down.
  • If the pin stops halfway or does not go in at all, do NOT force the pin, your threads are likely outside of the tolerance.

If the pin does not slide freely, it is advised to have your barrel inspected by a competent gunsmith. 

This device is not an absolute guarantee of concentricity. 

The pin is made of O-1 tool steel, hardened to 50 Rockwell C, then ground to size. This pin is ground to 0.2178. It should fit most all 5.56 rifling. The gage body is made of 4140PH and Parkerized. 

*The pin is made of steel and will rust if not maintained with a light coating of oil.

*Will not fit .22 rimfire barrels.


Product Reviews

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  1. Don’t leave thread concentricity to chance! 5 Star Review

    Posted by on 3rd Sep 2019

    This is a well-made tool that comes with a clear set of instructions. It’s a good idea to check your barrel threads before putting on your muzzle device, or suppressor. I’m happy to have this in my toolbox.

0.10 LBS


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