This is a Fusion Firearms Pro-Series Premium, Forged 1911 colt style Precision Pro Series, Serrated Slide stop in heat treated Forged alloy steel with Carbon Black Matte finish. For 45 ACP Caliber pistols Precision machined from Bar Stock. This is a very high quality part, No-MIM. .1995 - .2005" diameter shaft to help aid in precision lock-up. The Best of the Best in 1911 performance parts, Great product for new build 1911's and rebuild projects.