The ZEV Technologies Stainless Steel replacement guide rod allows you to change spring weights to tune your pistol to a particular load. The guide rod is designed with a replaceable head that can be changed if/when necessary thus extending the usable life of the part. The guide rod can also be run captured or un-captured. The ZEV Stainless Steel Guide rod is compatible with Gen 4 Glock with the use of guide rod reducing ring. Notes:Recommended usage of either an ISMI recoil spring in a corresponding correct weight for your pistol.ZEV Guide Rods are NOT Compatible with Glock Factory Guide Rod Springs.If you plan to use this Guide rod with a Generation 4 model Glock you must also use a Generation 4 reducer DISCLAIMER: This product is not manufactured, authorized, endorsed, or warranted by GLOCK. GLOCK does not warrant or represent that this product is compatible with GLOCK pistols.