- Additionally, we are now offering an RXM 4.5" threaded barrel accessory kit. This Genuine Ruger® Factory Accessory is compatible with Ruger RXM pistols originally equipped with a 4'' non-threaded barrel. The factory-manufactured, threaded alloy steel barrel accepts any 1/2''-28 (Class 2A) muzzle device. This kit contains a factory-manufactured alloy steel barrel with black nitride finish for optimal fit and function. Installing the threaded barrel is quick and easy with no gunsmithing required. Thread protector and threaded barrel guide rod assembly included