The Otter Creek Labs OPS/AE O.T.B. Adapter is a one-piece Over-The-Barrel (OTB) adapter for the Ops Inc 12th model, AEM5 and OCM5. Made from H900 heat treated 17-4 steel this one piece adapter will allow you to mount your silencer to any barrel with 1/2A-28 threads that is .75 OD or less with a minimum of 2.95-3 inches of exposed barrel. Made with integrated wrench flats in the rear for easy installation or removal with any adjustable crescent wrench. Mounting requirements for OTB adapter: 1/2A-28 barrel threads OD of 0.75" or less 2.95" of exposed barrel