Since the rotating spindle is uniformly tapered and the corresponding recess in the tool is tapered the same, until they come into intimate contact, the spindle does not grab the tool. When it does, the metal in the spindle compresses or the metal in the tool expands or more likely both. To get the tool to hold on tight, you tap it onto the spindle. To release it you tap it the other way. The principle is the same as a log-splitter that is, the horizontal component of force gets very great as you approach parallelism due to the outward force vector.
Typical lathes are around four to seven per cent.
There was no consistency among manufacturers and the numbers were essentially meaningless. So they made two important changes to the terminology and the standards. The second was in the standardization of the sizes. Other endodontic devices were also standardized, e.g. pluggers, paper points and gutta percha points. The second important standard they agreed to nominal sizing and its terminology.