Overall Length: 3.052" Rod Diameter: .25" Guide Rod Material: Stainless Steel Reverse Plug Material and Finish: Blued Carbon Steel Recoil Spring Type: 14lb Flat Wire Commander Spring for 9mm [ISMI Spring] This kit reduces recoil and increases longevity of the spring system in Springfield 4" guns. If you have a .45 ACP or .40 S&W you will need the kit with the 22lb flat wire spring available here. The kit includes a 1/4" guide rod, reverse plug and ISMI flat recoil spring. All systems use a 1/4" guide rod made from solid barstock with a take down hole. Reverse plugs are Blued carbon steel. Meant fo Mfg: Egw