Evolution Gun Works GI Arched Mainspring Housing w/Lanyard Loop WWII 1911s Steel Blued Carbon Steel Blue. 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. This item will fit 1911 Government and Commander frames it will not fit STI's or short grip frames.Our G.I. Arched Mainspring Housing is machined from carbon steel barstock. Specifications for Evolution Gun Works GI Arched Mainspring Housing: Manufacturer: Evolution Gun Works Color: Black Finish: Blue Fabric/Material: Steel Design/Pattern: Arched/Serrated Gun Make: 1911 Platform Gun Model: 1911 Condition: New Package Contents: Evolution Gun Works GI Arched Mainspring Housing What firearm models does the manufacturer say Evolution Gun Works GI Arched Mainspring Housing is compatible with? The manufacturer suggests that Evolution Gun Works GI Arched Mainspring Housing is compatible with 1911Evolution Gun Works 11441: GI Arched Mainspring Housing with Lanyard Loop WWII 1911s Steel Blued Carbon Steel Blue