Ring Type Joint Flanges (RTJs) come in a variety of sizes, with the most common being Class 150, Class 300, Class 600 and Class 900. Each size has its own unique dimensions, which are specified by the American National Standard Pipe Threads (NPT). Depending on the size, RTJ flanges may have either a raised face or a flat face. Generally speaking, a 4-inch RTJ flange will measure 5 to 6 inches across the bolt circle and 4 inches from the inner bore to outside diameter. The thickness of an RTJ flange also depends upon its size; for instance, a 4-inch RTJ flange can range from 0.75 to 1 inch thick. Not only can Ring Type Joint Flanges be used in moderate temperature services such as water and chemical piping systems, but they are also suited for higher temperature services like natural gas lines and refining pipeline applications.