See flangeless for a definition. this type of valve is very economical from a manufacturing and stocking standpoint because a valve that is rated as a 600# ANSI valve can also be used between 150# and 300# ANSI flanges thus eliminating the need to manufacture three different valve bodies or stock three different valve bodies. The down side is that valves with flangeless bodies are not acceptable in certain applications - particularly in refinery processes.