0.9 centimeters? i think?
The millimeters on a ruler are the tiny lines in between each centimeter
nine millimetershalf of a half of a centimeter
Millimeters, it is the size of the bullet.
If you are using a ruler marked only in inches then the best sub-division of an onch which approximates to 5 millimetres would be one-fifth of an inch. There are 25.4 millimetres in 1 inch.