Perfect Thread Length : A design length from the end of pipe or coupling to a specified location. For buttress thread this is an L7 . Some threads may have unfinished crests. (RP 5B1)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}