M2 Armament Group AR-15 Mil-Spec Lower Parts Kit Black. Purpose-built for cost-conscious rifle builders custom armorers and general-purpose carbine projects this all-in-one hardware package provides every small part spring detent and pin required to complete a mil-spec lower receiver assembly. Specifications for M2 Armament Group AR-15 Mil-Spec Lower Parts Kit: Manufacturer: M2 Armament Group Color: Black Weight: 7 oz Package Contents: M2 Armament Group AR-15 Mil-Spec Lower Parts Kit M2 Armament Group M2-LPK-15: AR-15 Mil-Spec Lower Parts Kit Black