movement along one rotational degree of freedom about the drive axis d the helical openings 70 are adapted for receiving therein a portion of the sockets 48 with the orientation of the helical openings 70 and the fact that the drive mode external sleeve 66 is kept from moving in translation on the drive axis d a rotation of the drive mode external sleeve 66 will cause the internal sleeve 60 to translate with respect to the drive axis d as the sockets 48 will move upward or downward in the helical openings 70 as mentioned earlier a translation of the internal sleeve 60 on the drive axis d will have the drive rollers 30 rotating in the z axis the reverse mode external sleeve 72 has an internal diameter slightly greater than the external diameter of the drive mode external sleeve 66 so as to be in sliding contact therewith the reverse mode external sleeve 72 also has obround openings 74 which are equidistantly spaced on the periphery of the reverse mode external sleeve 72 helical openings 76 are positioned between adjacent ends of obround openings 74 however when compared with the drive mode external sleeve 66 the helical openings are.