Machined from: Solid Bar Stock Steel Compatible with: Kimber, Colt, and other full-size or commander-style 1911s 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 EGW's 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.