Combat Armory Thread Protector 1/2 x 28 (9mm & .357SIG)) The Combat Armory thread protector is manufactured from solid Aerospace Materials. Designed to protect your threaded barrel when an accessory is installed. This thread protector is common to 9mm caliber threaded barrels. (including 9mm conversion threaded barrels) Fits all 1/2 x 28 threaded barrels.