The 6" Ames Colt series C-300 Double Check Detector Assemblies began production in 2000 under the Hunter name. In 2002, Ames bought the rights off of Hunter and is still manufacturing the devices. The body is constructed of stainless steel. The Colt Series has become a top seller of Ames due to the light weight design and short lay lengths. It is also offered in a number of configurations with many valve options. To access the check assemblies there is a stainless steel sleeve that will slide open. You must unthread the #3 test cock then slide the cover. The Colt uses two self contained cam checks that use a tri-link check mechanism. Numerous repair parts are available for the Colt series devices, including rubber parts and complete parts. The C-300 was designed for fire service line as it features a metered bypass assembly. The bypass backflow device will be 3/4" but Ames used different models over the years. The first 2 years used Flomatic DCVE. After that they may feature an Ames 2000B-M3 or Watts 007M3. Be sure to identify your bypass device before ordering parts. There are no special tools required for service.