Abstract: A device for cutting at least one longitudinally extending slit in the wall of a tub, which device comprises a substantially tubular thruster unit and a substantially tubular cutter unit arranged in axial alignment, which thruster unit includes a first gripping means for preventing the tube, which has been introduced through the bore of the thruster unit into the bore of the cutter unit, from moving relative to the thruster unit in a direction away from the cutter unit and which cutter unit includes at least one tooth for cutting a longitudinally extending slit in the wall of said tube and, between said tooth and the thruster unit, a second mechanism for preventing the tube from moving relative to the cutter unit in a direction towards the thruster unit; a double handled mechanism for urging the cutter unit in an axial direction relative to and a limited distance towards and away from the thruster unit; and, associated with each unit, adjustable mechanism for releasing the associated gripping mechanism.