LBE Unlimited AR15 Castle Nut Manganese Phosphate Coated 4140 Steel. These AR15 Lower Parts from the experts at LBE Unlimited are manganese phosphate coated to resist corrosion and abrasions making them the perfect tool for the job. This LBE Unlimited AR15 Steel Castle Nut serves as a replacement for the front sight base castle nut and fits most AR-15 rifles. Pick up the LBE Unlimited AR15 Castle Nut for your workbench to ensure your firearm is functioning at its highest capacity. Specifications for LBE Unlimited AR15 Castle Nut: Manufacturer: LBE Unlimited Gun Model: AR-15 Package Contents: LBE Unlimited AR15 Castle Nut What firearm models does the manufacturer say LBE Unlimited AR15 Castle Nut is compatible with? The manufacturer suggests that LBE Unlimited AR15 Castle Nut is compatible with AR-15LBE Unlimited LBARCNUT: AR15 Castle Nut Manganese Phosphate Coated 4140 Steel