STAINLESS STEEL GUIDE ROD ONLY. You are purchasing the guide rod only. The recoil spring must be purchased separately. The S/S guide rod can be used with the original factory recoil spring or ISMI "flat wound" recoil spring. If you intend to use a Wolff "round wound" recoil spring you must install a washer behind the screw tip. Factory recoil spring weights: 17 lbs. on all G17,17L,22,24,31,34,35,37 Pistols 18 lbs. on all G19,23,32,38 Pistols 17 lbs. on all G20,21,21SF Pistols The stainless-steel guide rods provide a decisive advantage for all Glock owners. Special features include a rigid stainless-steel body that improves lock up by completely removing "guide rod flex". The hex screw removable tip allows the user to choose various spring weights that will calibrate the ammunition to his/her gun. Used by Law Enforcement and competitive shooters worldwide, will not chip or crack like the factory plastic guide rods are prone to do. Will not damage or wear your polymer frame and guaranteed to provide a lifetime of reliable service. *We recommend the use of Blue Loctite on the hex screw threads. This will provide a firm hold and still allow easy removal when necessary. Allen wrench provided.