Abstract: A tool for shell or slab-splitting rocks or for wedging rocks in tunnels comprising a hydraulic/pneumatic cylinder (2) with an internal first piston (3), said first piston (3) being provided with a hydraulic/pneumatic pressure by supplying a fluid, preferably oil, through a supply conduit (1), and the power from the piston (3) is transferred to a wedging device comprising a wedge (10) which may be displaced between wedge holders (11, 12) being located in a drilled hole (13), the piston (3) being connected to a piston rod (7) which runs to a second internal piston (8) being located in a piston housing (6), the power from the first piston (3) being transferred to the piston (8), for thereby pressing the wedge holders (11,12) towards the surrounding rock, and creating a crack therein at the appropriate pressure wherein the wedge (10) is located parallel to the lengthwise axis and peripherally in relation to the hydraulic/pneumatic cylinder (2) is disclosed.