This sitar kuti has been broken. Since it is an old kuti, the ball is a little bit smaller than recently made new samples.
So, either you change the whole set, or you repair the broken specimen.
Cut the ball from the pen.
Drill a hole in the ball.
Make this hole square.
Find a new pen, make one end equally square.
Make it fit properly in the ball.
Apply glue and let dry.
Finish according to original.