Wilson combat's 17# flat-wire recoil spring 5" .45 acp chrome silicon 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).Our testing has indicated that these springs have a service life up to ten times greater than conventional coil springs.Features improves cycling and overall operation .250" rod diameter; compatible with standard recoil spring plug and with shok-buff recoil buffers.Finish: SilverType: Recoil SpringModel: Flat Wire Recoil SpringDimensions: .250 x 5"Size: Full SizeMaterial: Chrome Silicone Steel