Tools are previewed within the Tool Library when selected. The distance between the gridlines is fixed and allows you to quickly get a rough estimate of the tool size.
2.5 mm drill
8 mm drill
For metric tools, the distance between the thin gridlines is 1.0 mm and 10 mm between the tick lines. For inch tools, the distances are 1/16 inch and 1.0 inch, respectively.
By moving the mouse pointer over the image, a zoom is applied to the tool preview focusing on the cutter and fitting it to the preview area.
2.5 mm drill
8 mm drill