Evolution Gun Works Recoil Spring ISMI Round Wire Commander 4 1/4 20 lb. ISMI is a contractor of the U.S. government and produces springs used in machine guns with incredibly high cycling rates. Also the creator of ISMI springs obtained his knowledge from extensive research in the development of springs used in Indy car racing. Specifications for Evolution Gun Works Recoil Spring ISMI Round Wire Commander: Manufacturer: Evolution Gun Works Color: Black Gun Make: Colt Gun Model: Colt Commander Weight: 20 lb Package Contents: Evolution Gun Works Recoil Spring ISMI Round Wire Commander What firearm models does the manufacturer say Evolution Gun Works Recoil Spring ISMI Round Wire Commander is compatible with? The manufacturer suggests that Evolution Gun Works Recoil Spring ISMI Round Wire Commander is compatible with Colt CommanderEvolution Gun Works 10662: Commander 4 1/4 Recoil Spring ISMI Round Wire 20 lb