Black Crested Thread 1 : A thread that does not have a full crest because the original (black) mill surface has not been completely removed. (Bul 5T1, RP5A5)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}