MagPump 9mm Double Stack Magazine Retainer for Walther P99Q Black MR-WALTHER P99Q. Your purchase of the 9mm Luger includes a set of six adaptable retainers to fit pistol models in SIG Smith & Wesson Springfield Armory CZ and Ruger. Retainers are designed to fit double stack magazines for popular 9mm models. Specifications for MagPump 9mm Double Stack Magazine Retainer: Manufacturer: MagPump Color: Black Package Contents: MagPump 9mm Double Stack Magazine Retainer MagPump MR-WALTHER P99Q: 9mm Double Stack Magazine Retainer for Walther P99Q Black