Hole Axis : A line through the center of the hold, generally considered to be the centralized position that would be taken by a stiff tubular member inserted through that section of the hole. (Bul D20)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}