Blocks, Crown and Traveling : The fixed upper and movable lower blocks respectively of the block and tackle assembly on a rig that raises and lowers the drill string or tubing. (RP 54)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}