HAO's HK416A5 Enhanced Castle Nut for UN18 thread stock. 

Made from S45C steel bar and black oxided, which is fully compaitble with RS/ PTW stock thread. 
 

HK416A5 Enhanced Castle Nut

$15.00Price
  • S45C carbon steel 
  • CNC turned 
  • Black Oxided 
  • UN18 thread (PTW/RS compatible)