Modern-day handguns are filled with springs that ensure reliable functioning through thousands of rounds, but springs are wear components that must be replaced at intervals to ensure proper functioning of your handgun. This Apex Tactical Slide Maintenance Kit includes all the springs you need to keep your FN 509 handgun running right. Each spring in the Apex Tactical FN 509 Slide Maintenance Kit is designed as a direct, drop-in replacement for the OEM springs in your handgun slide. All of the springs are designed to work for 10,000 rounds before needing replacement. The springs in this Apex Tactical Slide Maintenance Kit will work for all FN 509 models, including the Midsize, Tactical and Midsize MRD. The kit will not work with the FNS, FNS Longslide or the FNS Compact.