This is a balanced kit containing two SHOK-BUFF® buffers and one heavy duty recoil spring. The SHOK-BUFF® should be changed out every 1,000 rounds and the recoil spring every 2,000 rounds. When the SHOK-BUFF® buffers are gone, it's time for a new kit. It's a great way to remember your recoil spring changes. The recoil springs have a closed coil on one end to help them seat firmly on the guide rod. The closed coil end can be identified by its two close windings and narrow inside diameter. For proper installation, slide the closed coil end over the guide rod stem, this will leave the open end of the spring against the recoil spring plug. Improper recoil spring installation can lead to erratic cycling and possible guide rod damage.