Abstract: A thread structure for interconnecting two elements in a percussion drill string comprising an interior cylindrical thread and an exterior cylindrical thread. The threads have abutting flanks which are straight along their abutting contact portions. The clearance (a) between the bottom portion of the exterior thread and the crest portion of the interior thread is large enough to ensure that contact does not arise at said clearance when the threads are worn.

Abstract: Drilling means of the type having a pilot bit, a reamer and a guidemember mounted in the bottom end of the casing tube, and which transmits impacts to the casing. The guide member is snugly enclosed in the thickened mouth portion of the casing tube and has a plurality of channels which are segments of a spiral through which the drilling debris is discharged upwardly to the casing tube.

Abstract: A drill tool for rotary and/or percussion drilling with drill rod means (14) within casing tube means (15) comprises a centric cutting bit (11) and an eccentric reamer cutter (12), both provided with hard metal inserts. For purposes of obtaining a life of the drill tool as long as possible the first frontal insert (23) on the reamer cutter (12) is positioned in front of the first peripheral insert (18) when seen in the rotational direction (D) during drilling, and the centric cutting bit (11) provided with more inserts on the half (38) of its front surface opposed to the reamer cutter (12) during drilling than on the other half (39).

Abstract: Drilling means of the type having a pilot bit, a reamer and a guidemember mounted in the bottom end of the casing tube, and which transmits impacts to the casing. The guide member is snugly enclosed in the thickened mouth portion of the casing tube and has a plurality of channels which are segments of a spiral through which the drilling debris is discharged upwardly to the casing tube.