MAST (Also Known As GANTRY) : A frame hinged at or near the boom hinge for use in connection with supporting a boom. Head of mast is usually supported and raised or lowered by the boom hoist ropes. (Spec 2C)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}