Product Info for Maxim Defense Industries JP Silent Captured SpringThe JP Silent Captured Spring Systems are manufactured exclusively for Maxim Defense Industries to work with the Maxim Defense CQB Stock System. Choose from the standard/carbine weight, heavy weight and 9mmweight Silent Captured Spring Systems. The JPSilent Captured Spring Systems require an open channel in your bolt carrier group assembly for the guide rod to pass during fire. Note:DO NOT MODIFY A BCG TO MAKE IT COMPATIBLE. DO NOT REMOVE THE WEIGHT FROM 9MM BCGS. JP DOES NOT RECOMMENDED FOR SELECT FIRE.Specifications for Maxim Defense Industries JP Silent Captured Spring:Color: Grey/BlackFabric/Material: Tungsten and Stainless SteelSpecifications for Maxim Defense Industries JP Silent Captured Spring:Manufacturer:Maxim Defense IndustriesColor:Grey/BlackFabric/Material:Tungsten and Stainless SteelCondition:NewCountry of Origin:USAFeatures of Maxim Defense Industries JP Silent Captured SpringFeatures of Maxim Defense Industries JP Silent Captured SpringJP Silent Captured Spring - XS, Tungsten, Stainless Steel, ONLY Fits: Maxim Defense CQB Stock/Brace.Package Contents:Maxim Defense Industries JP Silent Captured SpringMaxim Defense Industries JP Silent Captured SpringMaxim Defense Industries MXM-47570: JP Silent Captured Spring - Standard, Grey/BlackMaxim Defense Industries MXM-47571: JP Silent Captured Spring - Heavy, Grey/BlackMaxim Defense Industries MXM-47572: JP Silent Captured Spring - 9mm, Grey/Black