Echo Zulu Castle Nut Stake your AR’s castle nuts faster, safer, & more consistently with Tango Uniform’s new Echo Zulu Castle Nut System. The patent pending EZ castle nut is made from premium 4140 PH alloy steel and finished in long duration, diamond hard black nitride. It was precision machined on a modern Swiss CNC lathe, to tolerances that meet or exceed the mil-spec TDP, including true class 3 threads. The EZ castle nut features eight co-linear wrench & staking notches, allowing for easier visual alignment, and multiple staking locations with even the largest end plates.