Evolution Gun Works STI Mainspring Housing 25 LPI for 1911 Carbon Steel Blued Finish. Pins and springs do not come with this part. You can use the pins and springs from your original mainspring housing or purchase new parts from us.This mainspring housing makes a great replacement for plastic mainspring housings.This is our premium mainspring housing designed and made by EGW. Fully machined from bar stock sandblasted and then hot blued. This item will fit 1911 Government and Commander frames. It is a flat mainspring housing. Specifications for Evolution Gun Works STI Mainspring Housing 25 LPI: Manufacturer: Evolution Gun Works Color: Black Finish: Blue Fabric/Material: Steel Gun Make: 1911 Platform Gun Model: 1911 Condition: New Package Contents: Evolution Gun Works STI Mainspring Housing 25 LPI What firearm models does the manufacturer say Evolution Gun Works STI Mainspring Housing 25 LPI is compatible with? The manufacturer says that Evolution Gun Works STI Mainspring Housing 25 LPI is compatible with 1911Evolution Gun Works 11460: STI Mainspring Housing 25 LPI for 1911 Carbon Steel Blued Finish