Fusion Firearms, 1911 Officers size Checkered Mainspring housing MagWell in carbon Steel, Black Oxide finished It includes a Bar stock machined Mainspring housing & MagWell, CNC Machined parts from Carbon Steel Bar stock, NO-MIM. These are Top Quality Professional Series Parts; Made from the best materials and processes available in today's market. 2 piece Dovetail base well with set screw. This is a Pro-Series Checkered pattern 25 LPI mainspring housing. All Machined from Carbon steel bar stock and great looking and feeling cut checkered pattern. These are as nice as they get. Will work for most all Officers size and Many Micro style size 1911 pistols.