This is a customizable (parametric) 3D printable writing aid. The pen ball makes it easier to grip a pen, pencil, or other writing utensil and may be useful for someone who has difficulty holding a pen or pencil directly. The diameter of the ball and the writing utensil diameter can be customized to fit the user. Usage: A pen, pencil or stylus is inserted through the pen ball and is fixed in place by tightening a screw. The ball is held in the hand to make it easier to write. This set of 3 50mm diameter balls is sized for small hands. They include pen holes of 5, 10.5 and 12.5 mm. **Replacement cost is $30.00