An apparatus for manipulating, such as machining, and especially cutting tubular and round-bar type pieces, said apparatus comprising a clamping mechanism adapted to be fastened to said workpiece rotatably therearound and said clamping mechanism configured to be attached thereto a tool unit, which is provided with adjustment means for displacing said tool unit relative to the clamping mechanism towards or away from the workpiece, and said clamping mechanism comprising a frame element and first and second arms (6, 7) extending therefrom, said arms (6, 7) being coupled at one end to the frame element of the clamping mechanism and each arm (6, 7) has its free end fitted with a contacting member (15, 16, 31, 32) configured to contact the surface of the workpiece, whereby the apparatus comprises: - a first movable guiding member (28, 29) to which said first arm (6, 7) is coupled, and a second movable guiding member (28, 29) to which said second arm (6, 7) is coupled, wherein said guiding members (28, 29) are configured, when moved away from each other, to move the first and second arms (6, 7) and thereby said contacting member (15, 16, 31, 32) coupled with the arms (6, 7) away from each other and vice versa, characterized in that the apparatus comprises: - at least two supporting bars (50, 51) elongated through said guiding members (28, 29), and - the first supporting bar comprising a first threaded portion, said first threaded portion comprising a first coupling means, and the second supporting bar comprising a second threaded portion, said second threaded portion comprising a second coupling means, where said first threaded portion is configured to move said first coupling means along said first supporting bar and said second threaded portion is configured to move said second coupling means along said second supporting bar, when said first and second supporting bars (51, 53) are rotated, where - the first arm and the first coupling means are functionally coupled to each other by a first suspension arm, and the second arm and the second coupling means are functionally coupled to each other by a second suspension arm, and - said at least two supporting bars are coupled to each other so to be rotated at the same time. - a first movable guiding member (28, 29) to which said first arm (6, 7) is coupled, and a second movable guiding member (28, 29) to which said second arm (6, 7) is coupled, wherein said guiding members (28, 29) are configured, when moved away from each other, to move the first and second arms (6, 7) and thereby said contacting member (15, 16, 31, 32) coupled with the arms (6, 7) away from each other and vice versa, - at least two supporting bars (50, 51) elongated through said guiding members (28, 29), and - the first supporting bar comprising a first threaded portion, said first threaded portion comprising a first coupling means, and the second supporting bar comprising a second threaded portion, said second threaded portion comprising a second coupling means, where said first threaded portion is configured to move said first coupling means along said first supporting bar and said second threaded portion is configured to move said second coupling means along said second supporting bar, when said first and second supporting bars (51, 53) are rotated, - the first arm and the first coupling means are functionally coupled to each other by a first suspension arm, and the second arm and the second coupling means are functionally coupled to each other by a second suspension arm, and - said at least two supporting bars are coupled to each other so to be rotated at the same time.