Full-interlocking Kelly bar is composed of three weld-on ribs with continuous  concave and convex  keys . During the drilling process, the downward thrust is transmitted to drill bucket directly by rotation power of  Rotary head inner ribs and Kelly bar outer ribs at any time . This type of Kelly bar is the best one of transferring pressure at present , especially for hard ground and frozen oil layer construction. In the drilling process , every continuous steps can form pressure point to reduce  wear and tear of local pressurization key lines, also to avoid the stick problem that Kelly pipe is deformation always in a part pressurization.