KAC - Knight's Armament Company URX 4 Series Rail Handguards - M-LOK, IBN


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KAC - Knight's Armament Company URX 4 Series Rail Handguards - M-LOK, IBN


The Knight's Armament Upper Receiver Extending Rail system, or URX, is now in it's 4th generation and being offered in M-LOK.  The URX 4 is a continuous top-rail system that utilizes Magpul's M-LOK mounting system. 

This rail system is built stronger and more stable compared to previous designs, and the modular design, with M-LOK slots on 7 sides of the rail.  Knight's unique Intergal Barrel Nut (IBN) moutning configuration is a modular and servicable mounting system that optimizes the rail system's strength and stiffness.  The rail itself acts as a barrel nut on the IBN system, a simpler solution than previous iterations that requires less specialized tools to install and maintain.

Available in the following lengths (and associated weights): 

  • 8.5" (8.3 oz)
  • 10.0" (9.3 oz)
  • 10.75" (TBD)
  • 13.0" (11.3 oz)
  • 14.5" (12.3 oz)


  • Inner Diameter:  1.53"
  • Outer Diameter:  1.69"
  • Rail Height:  2.07"


Manufacturer Knights Armament Company
Shipping Restriction ITAR/Export Restricted
MSRP $271.66
Weapon Model AR15/M16
Barrel Rest Free Float
Material 6061-T6 Aluminum
Material Finish Type III Hard Coat Anodized
Color Black


Customer Reviews

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Overall Customer Rating

Based on 1 review(s) (1)

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The Envy of My Friends

Posted by Sean | (Posted on 12/5/2020)

I picked up this rail to complete a 13.7" build I had been working towards for awhile. The rail was recommended to me by Jaxon, who was incredibly helpful in making sure that everything fit cleanly during a mockup.

The URX4 is as sturdy as they come, and while a bit of a challenge to install, it looks flawless. Not only does it look beautiful, I have zero problems running the absolute crap out of it. The form, fit, and function of this rail, a 13.7" from SOLGW, and a Surefire can is unmatched.

I have absolute faith in the strength of the rail for anything that might be thrown at it. Years ago as a kid, my grandfather told me to buy once and cry once. He was referring to car parts, but it's also applicable here.


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