Evolution Gun Works Mainspring Housing 25 LPI Undrilled Kimber Colt 1911s Steel Stainless. The checkering on this mainspring housing helps get the weight in the right place and gives you good traction.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. It is a flat mainspring housing. Specifications for Evolution Gun Works Mainspring Housing 25 LPI Undrilled: Manufacturer: Evolution Gun Works Fabric/Material: Steel Design/Pattern: Checkered Gun Make: Colt Gun Model: 1911 Commander 4.25in Additional Features: Undrilled Condition: New Package Contents: Evolution Gun Works Mainspring Housing 25 LPI Undrilled What firearm models does the manufacturer say Evolution Gun Works Mainspring Housing 25 LPI Undrilled is compatible with? The manufacturer suggests that Evolution Gun Works Mainspring Housing 25 LPI Undrilled is compatible with 1911 Commander 4.25in Colt 1911 Government 5inEvolution Gun Works 11410: Mainspring Housing 25 LPI Undrilled Kimber Colt 1911s Steel Stainless