According to a prior art solution to secure that a certain thread joint is loosened first, see SE 433097, threads with different pitches or cones are used to achieve a thread joint which is substantially more difficult to loosen than the other. These solutions have the drawback that one has to use nonstandardized parts. At use one also has to keep track of which end is which in order to achieve correct connection.

The present invention, which is defined in the subsequent claim, aims at avoiding the above drawbacks through using substantially the same thread in both joints and that the joint which should be more difficult to loosen by means of a mechanical joint is prevented from loosening when the rock drilling machine and the rock bolt are separated.

An embodiment of the invention is described below with reference to the accompanying drawing in which fig 1 shows a coupling sleeve according to the invention. Fig 2 shows a section according to 2-2 in fig 1 and with rock bolt and rock drilling machine connected.

Fig 3 shows a section according to 3-3 in fig 1.

The coupling sleeve shown in the drawing comprises a first part 3 provided with an internal thread 4 to which a threaded rock bolt 1 is connectable. The threaded rock bolt is provided- with a not shown drill bit for drilling the hole in which the rock bolt is to be anchored. The coupling sleeve also comprises a second part 5 provided with an internal sleeve 6 to which a rock drilling machine is connectable. In the drawing the shank adapter belonging to the rock drilling machine is shown. The second part 5 comprises a longitudinal slot 7 and clamping means 8. The clamping means are in the shown examle three screws 8 by means of which the slot 7 can be pressed together so that the second part 5 can be squeezed about the shank adapter of the rock drilling machine 2. The second part 5 is provided with a groove 9 so that deformation of the thread 6 at clamping of the second part 5 about the rock drilling machine 2 does not become dissturbing for the functioning. The coupling sleeve is also provided with a flange 10 against which the rock bolt 1 and the shank adapter of the rock drilling machine 2 rest. The impact energy of the rock drilling machine is transferred via the flange 10 to the rock bolt 1 when it is drilled into the ground in which the rock bolt is to be anchored. By means of the shown design it is secured that the thread joint between the rock bolt 1 and the thread 4 is the joint which is loosened when the connection between the rock drilling machine and the rock bolt is broken.