Lack of sufficient thread height (depth). This may be because of a "shaved" condition where an excess of metal has been removed form the root or crest, distorting the contour of the thread. (Bul 5T1, RP 5A5)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}