Fusion Pro-Series Aluminum alloy Light weight Mainspring Housing, for Officers size 1911. CNC Machined from aluminum alloy bar-Stock, With plain smooth back. Silver coated to resist corrosion. Will fit most all 1911 Colt Officers style pistols, Micro’s and Clones. All CNC machined in the USA,. No MiM, No Cast, ALL Solid CNC Machined Bar-Stock.