space between the shank 34 and the outer pipe 12 and which permit flushing medium to pass into the axial duct 10 of the drilling it 2 0060 fig7 and the detailed views on an enlarged scale in fig8 a 8 c 9 a 9 c and 10 show an alternative embodiment of the drilling system in which rotary forces are also applied to the drilling head 2 by way of the percussion string 13 u2032 the views on an enlarged scale showing individual parts in fig8 a 8 c show the two ends 19 u2032 and 20 u2032 of the rods 14 u2032 in this respect fig8 a is a view in longitudinal section showing the rod end 20 u2032 which is in the form of a ball socket and into which the rod end 19 u2032 which is in the form of a ball head is inserted fig8 b shows only the rod end 19 u2032 in the form of the ball socket as a plan view and two side views fig8 c shows the rod end 20 u2032 in the form of a ball socket as a plan view in longitudinal section and as a side view each rod 14 u2032 of the percussion string 13 u2032 includes a rear rod end 19 u2032 which is curved in the form of a ball head and on which are arranged projections 42 in the form of a star the front rod end 20 u2032 which is curved.