46 however are displaceable on these sleeves in the axial direction the arm ends are provided with rectangular sections 48 which cooperate with a freely rotatable friction disk 49 centrally located on the king pin 7 whereby the friction disk evidences a projecting annular surface on both sides which are determined as the actual friction surfaces the external arm extension with the push rods and the joint heads are not illustrated in fig1 and 13 in the event that the clamping force of the joint heads is to be varied then the two sleeves 8 46 and the corresponding push rod inner component 14 can be easily exchanged thus for example the arm which is fastened to a foot of the stand can cooperate with a sleeve which evidences a recess with a steeper abutting surface in comparison with the recess in the second sleeve which for example is determined for a work tool supporting arm at the clamping of the hand lever the stand supporting arm is more intensely locked than the work tool supporting arm through a corresponding selection of the shape and the slope of the abutting surfaces there can thus be influenced the clamping force and the.