Seam 01 : A longitudinal crevice in the rod which has been closed but without metallurgical bonding and has the appearance of a scratch or small longitudinal separation of the bar. (Spec 11B)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}