Place a recirculating-ball bushing on a shaft and what do you get? Frictionless movement of the shaft. But, create grooves along the axial length of the shaft that correspond to the radius of the bushing’s ball elements and you’ve got frictionless linear movement coupled with two important characteristics – those being anti-rotation torque transfer and higher load capabilities.
Now… that’s a ball spline. It combines a linear bushing (nut) that can now handle greater moment loads and, a shaft, which, unlike a rail, can be rotated when needed. It is perfect for high-speed motion and high-speed rotation.