Abstract: A motion converter used with an input element rotatable about an axis and an output element displaceable axially relative to the input element has an axially nondisplaceable support provided with a first external screwthread of predetermined diameter, pitch, and hand centered on the axis and a second external screwthread provided on the output element centered on the axis and of the same diameter and pitch as the first screwthread but of opposite hand. A roller having respective first and second ridged portions respectively meshing with the screwthreads has a mechanical coupling for maintaining the first and second roller portions aligned axially with each other.