A portable tool comprising a hollow body delimiting two chambers and comprising a shoulder and a barrel extending from the shoulder. A piston slides in the chambers and a stem is secured to the piston and is accommodated in the barrel. A C-shaped head with a first end forms a shoe which presses against the shoulder and in which is created a bore into which the barrel fits, and with a second end facing the free end of the stem. A fastening system comprises a channel on the barrel perimeter. Two sliders are slidably mounted on the shoe parallel to a plane of movement which is perpendicular to the axis of the barrel. Each slider has an arc shaped face and movable between a retracted position in which the face is accommodated in the channel and an extended position in which the face is outside the channel.