The PM237B 9mm magazine adaptor block easily installs in AR-15A(R) / M16 lower receivers to allow the use of 9mm ColtA(R) / SMG type magazines with 9mm upper receivers. The block is constructed of high strength polymer with steel hardware, roller, ejector, and bolt stop. Improved design allows quick install without the need to remove the bolt stop roll pin. 9mm magazine adaptor block Installs in AR-15A(R) lower receivers Allows the use of 9mm ColtA(R) / SMG type magazines with 9mm upper receivers Made of high strength polymer with steel hardware, roller, ejector, and bolt stop Quick installation without the need to remove the bolt stop roll pin Ma Mfg: Pro Mag