Wilson combat's flat-wire recoil spring kit .45 acp 17 lb.Recommended use- full-size 5".45 acp shooting 230 gr.Hardball equivalent or standard pressure jhp self-defense ammunition with a power factor of 175 000 to 195 000 (velocity x bullet weight = power factor).The average service life is 40 000 rounds.Improves cycling overall operation and recoil spring life.Compatible with standard recoil spring plug and shok-buff recoil buffers.Includes.250" rod diameter recoil spring guide and 17# flat-wire recoil spring.Finish: BlackType: Recoil Spring KitModel: Flat-Wire Recoil Spring KitDimensions: .250 x 5"Size: Full SizeMaterial: Chrome Silicone Steel