DIFF Subgroup
E21B 21/011 Full Title
Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor (freeing objects stuck in boreholes by flushing E21B31/03) > Arrangements for handling drilling fluids or cuttings outside the borehole, e.g. mud boxes
Of 3 combined children, 0 exist in both systems.
3 codes are CPC-only extensions.