screw ball or screw nut
How can be define ball in the nut on solidworks assembly? (Ball must be rotate and move.)
The basic way is to use screw mate. If you are using the ball screw in an assembly you should first have to mate the screw allowing it to have one degree of freedom( rotation along its axis), then you should use concentric mate to align both ball screw and nut in a common axis. Ball nut should also have only one DOF( translation along the common axis) so use necessary mates( parallel/ coincident ). Finally apply screw mate.