What is root clearance ?
The distance between the outside circle of a gear and the root circle of its mating gear (the gap) is called the root clearance.
This distance (the gap) is also called the root clearance, top clearance, bottom clearance or simply the clearance.
When the dedendum is 1.25m and the addendum is 1.00m, this difference of 0.25m provides the escape for the two gears to mesh without interference.
In the diagram below, "c" is the root clearance.
