The Stealth Recoil Spring comes with Red LOCTITE on the front metal stop and Blue LOCTITE for the bottom bumper, when reassembling we recommend reapplying LOCTITE. The Stealth recoil spring can be installed with or without a buffer retainer. The polymer bumper goes towards the rear of the firearm and the weight mass with the o-ring goes towards the bolt carrier. (9mm Bolt Carriers ONLY)For proper function of the SRS-9 in your 9mm rifle or pistol, the extra weight on the back of the bolt carrier needs to be removed. It is held in with a spring pin. Most bolt carriers have a rear opening of over .60″, there are a couple of bolt carriers in the market place that have a rear opening of under .60″ and will not function with the SRS-9.