thin, fine

This thread is thin.

この糸は細いです

The thread my mother uses is thin.

母がこの糸は細いです

The thread my mother uses for sewing is thin.

母が縫い物に使うこの糸は細いです

The thread my mother uses for sewing is thin so it doesn't damage the cloth.

母が縫い物に使うこの糸は服が傷まないように細いです

The thread my mother uses for sewing is thinner than my hair so it doesn't damage the cloth.

母が縫い物に使うこの糸は服が傷まないように私の髪の毛より細いです