Convert your standard mil spec ar 15, m4, m16 lower assembly to use 9mm and.40 s&w m&p and p320/p250 magazines.The mag-ad series adapters install in seconds.Boasting a last round hold open feature making them a breakthrough product and a must-have for law enforcement and civilian gun enthusiasts alike.Caliber: 9mm/40 S&WFinish: Type 3 Hard AnodizedMaterial: Aircraft Grade Aluminum