The present invention concerns a coupling (1) including a first part (2) and a second part (3), where the first part (2) includes a housing (4) with a displaceable locking ring (8). The locking ring having a locking device (9) for receiving and fixing a projecting part (5). The housing is provided with an internal cylindrical surface with an annular recess (11) arranged for accommodating the locking device (9). The locking ring is connected with a spring-biased locking unit (17) for moving and locking the locking ring in at least two positions in the housing (4). The locking unit (17) includes an insert (18) connected to the locking ring (8) at one end and at an oppsoite end is provided with a number of oblique teeth (23).