These precision-machined components are coated with WMD's ultra-tough NiB-X nickel boron finish for superior durability, corrosion resistance, and exceptionally smooth metal-on-metal contact. The coating allows the parts to function under extreme conditions with little or no lubrication, and gives carbon fouling nothing to adhere to, so cleanup is much easier than with ordinary finishes. Allows longer intervals between cleaning without loss of weapon performance. Mfg: Wmd Guns SPECS: Steel with nickel boron silver finish. Fits small-pin (.154") AR-15 lower receivers only.