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Forward Controls Design 4140 Billet Castle Nut - Black Nitride

Manufactured by Forward Controls Design
Manufactured by Forward Controls Design
3 Reviews
$17.00 $19.00

In Stock

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The original MIL-SPEC castle nut is a hard product to improve upon, but Forward Controls Design has proven it is not impossible. The CNF is based on the original technical data package specification for the castle nut but does offer several improvements. Deeper staking notches make for much more secure staking. Even installation is improved with the coarse serrations making threading it down to the endplate easier and more comfortable.


  • 4140 PH Steel construction
  • Tough black nitride finish
  • 25% longer staking notches
  • Additional notch added
  • Coarse serrations for easy installation

Military specifications require castle nuts to be staked in two locations to ensure the castle nut and buffer tube will not loosen without deliberate action, and FCD believes this is one of those points where less is definitely not more. Traditional MIL-SPEC castle nuts have 3 staking notches, the CNF features 4, ensuring at any time three are available to be used. Each notch has also been upgraded to a deep, 30-degree cut, making them 25% longer than MIL-SPEC to ensure enough material can be staked into the notch for secure installation. To make threading the castle against the end plate even easier, the outer edge features coarse serrations.

Forward Controls Design firmly believes in the elegance of simplicity. Not content to produce purely aesthetic components, they put function before form to create parts and accessories that actually improve the handling and function of your firearms. When you need parts that just work without complication, you need Forward Controls Design.
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BrandForward Controls Design
MaterialSteel - 4140 Chrome Moly
California Prop 65 warning

 WARNING: This product can expose you to chemicals, which are known to the State of California to cause Cancer and Reproductive Harm. For more information go to www.P65Warnings.ca.gov.

Ratings & Reviews

3 reviews

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Better Than Standard

by -

I will only buy these going forward. Nice finish and look. Most importantly is the extra staking notch (4 instead of 3) that this comes with over a standard nut. This is supposed to allow for 3 notches to be accessible for staking once the nut is torqued down. This was the case for the two I've used so far. Two notches naturally line up on the sides and one up top. Makes staking much easier. Definitely recommended.

Best Castle Nut Available


4041 Billet Castle Nut coated in Black Nitride what more could you ask for. There's 4 wrench slots instead of 3 and same is with the staking locations. Staking slots are also shallower and longer then standard Castle nuts. I put this on my 7 position receiver extension torqued to 35lbs and staked 1 location good and 1200rnds later it still hasn't moved. Also the cool dimples they have cut into the edge looks better then nothing. IMO this is probably the best or next to it for Castle nuts.

Best I've Used


This is the best castle nut I've used. The fit and finish are second to none, the slots fit your wrench near perfect allowing easy torquing to your needed spec, and when it's tight, it's tight (that's what she said). Don't let the price scare you, it's worth it.