Arduino Mega Controlled inverted pendalum Simmechanics problem

Dear all;

I want to control an inverted pendalum using Arduino Mega with PWM controlled DC gear motor. I want to use a ballscrew attached the DC motor and attach the nut to the mass. The pendalum is attached to the mass with a joint.The mass is to move right and left to stabilize the pendalum upright position. I wanted to use "Lead Screw" block to model the ball screw. But I couldn't interface between nut and mass. Which block should I use to represent the mechanical relation between screw and nut.

Thank You.