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’s square hole.

Apply glue and let dry.

Finish according to original.

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Surbahar Kuti Repair