 What's unique about this digging stick is that a bored stone, about 15 centimeters in diameter, is attached at the opposing end.
<fluency>  What's unique about this digging stick is that a bored stone, about 15 centimeters in diameter, is attached at the opposing end.
 What's unique about this digging stick is that a bored stone, about 15 centimetres in diameter, is attached at the opposing end.