With the medium torque type Ball Spline, the spline shaft has two to three crests on the circumference, and along both sides of each crest, two rows of balls (four or six rows in total) are arranged to hold the crest so that a reasonable preload is applied.
With the high torque type Ball Spline, the spline shaft has three crests positioned equidistantly at 120 degree, and along both sides of each crest, two rows of balls (six rows in total) are arranged so as to hold the crest.