DIFF Subgroup
E21B 17/1035 Full Title
Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Casings; Tubings > Wear protectors; Centralising devices
E21B 17/1035 Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Casings; Tubings > Wear protectors; Centralising devices