SCREW THREAD FOR A DRILL STRING ELEMENT

摘要

A drill element is disclosed in the form of a drill rod, a sleeve for coupling together two drill rods or a drill bit; the drill element having a single start internal or external cylindrical screw thread by which it is intended to be coupled to a further drill element in the assembly of a drill string for percussion or rotary/percussion drilling. The screw thread has a root and a crest which are interconnected through a main flank, an effective diameter selected from the range 25 millimeters to 65 millimetres and a pitch angle .alpha.. In a section of the screw thread taken on the longitudi-nal axis thereof, the main flank is flat or substantially flat and is inclined at a flank angle .beta. to a plane which is normal to the longitudinal axis. a is determined, or substantially so, from the formula where is in the range 0.36 to 0.46; .beta. is in the range of 30.degree. to 65.degree., and .alpha. as determined is not greater than 9.5.degree..