Sharpness is wonderful only for natirrill. V Grooving ensures that the chuck does not slip and reliably rotates. However, something was not written on the attached plastic part, there is no description in the maker catalog on the net, and the plastic protection ring is attached for preventing the shock at the time of penetration in the document of the other explanatory note. Finally I understood the content. I just threw it away unless I noticed it. If there is an explanation somewhere, it will be better.