Sons of Liberty Gun Works Castle Nut Class 3B Threads Black. The SOLGW Castle Nut is made from 17-4 Stainless steel which is nitride treaded for maximum corrosion resistance. The face of our Castle Nut is ground flat for maximum surface contact with an end plate and features 6 deep staking recesses for maximum material displacement and more holding force than previously possible. The rear is also beveled between the drive notches for comfort. The SOLGW Castle Nut is machined with Class 3B threads for maximum thread engagement and rock solid security. Lastly the Castle Nut is extended beyond the typical mil-spec length for added material strength at the junction of the lower and the receiver extension (buffer tube); a potential weak spot. This makes it compatible with Intermediate/A5 length extensions only as it may prevent some stocks from fully collapsing on carbine length tubes. Specifications for Sons of Liberty Gun Works Castle Nut: Manufacturer: Sons of Liberty Gun Works Color: Black Fabric/Material: 17-4 Stainless Steel Finish: Nitride Features of Sons of Liberty Gun Works Castle Nut 17-4 Stainless Steel Nitride Treated Class 3B threads 6 Deep staking notches Extended Length Package Contents: Sons of Liberty Gun Works Castle Nut Sons of Liberty Gun Works SOLGW-CASTLENUT: Castle Nut Class 3B Threads Black