Mechanical pencil features a three-gear rotation mechanism that rotates the pencil lead every time it touches paper to provide a smooth and consistent writing experience. The Nano Dia lead is infused with millions of nanodiamond particles and silicone oil for a strong lead that produces darker and smoother lines. Refillable design and replaceable eraser stretch the limits of a mechanical pencil for lasting use. Mechanical pencil is designed for use with 0.5mm lead.