In Version R the spindle is axially fixed and linear motion is transmitted to the running nut
by rotation of the spindle. The nut must  be secured against rotation by fixing to the item or mechanism being moved.

In Version S (rising spindle) the spindle provides the linear motion. In this design the spindle moves axially through the screw jack. Rotation of the spindle must be prevented; usually by fixing the end of the spindle to the item being moved.
In Version SA a travel limiter is fitted to prevent overtravel of the spindle.
In Version SV spindle rotation prevention is included.
In Version SVA both overtravel and spindle rotation prevention is provided.